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 $96.97   11.661%   $108.2777   $108.28   $108.30   $108.30  
  Purchase #2 $172.79   13.209%   $195.6138   $195.61   $195.60   $195.60  
  Purchase #3 $204.87   3.867%   $212.7923   $212.79   $212.80   $212.80  
  Purchase #4 $181.80   9.270%   $198.6529   $198.65   $198.65   $198.70  
  Purchase #5 $226.97   10.162%   $250.0347   $250.03   $250.05   $250.00  
  Purchase #6 $212.66   9.122%   $232.0588   $232.06   $232.05   $232.10  
  Purchase #7 $60.46   8.365%   $65.5175   $65.52   $65.50   $65.50  
  7 purchase totals = $1,156.52       $1,262.9477   $1,262.94   $1,262.95   $1,263.00