Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.93   13.270%   $247.982   $247.98   $248.00   $248.00  
  Purchase #2 $170.45   13.216%   $192.9767   $192.98   $193.00   $193.00  
  Purchase #3 $204.45   6.867%   $218.4896   $218.49   $218.50   $218.50  
  Purchase #4 $134.79   8.747%   $146.5801   $146.58   $146.60   $146.60  
  Purchase #5 $214.44   4.732%   $224.5873   $224.59   $224.60   $224.60  
  Purchase #6 $184.31   10.727%   $204.0809   $204.08   $204.10   $204.10  
  Purchase #7 $229.72   8.132%   $248.4008   $248.40   $248.40   $248.40  
  7 purchase totals = $1,357.09       $1,483.0974   $1,483.10   $1,483.20   $1,483.20