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 $231.88   6.113%   $246.0548   $246.05   $246.05   $246.10  
  Purchase #2 $201.96   5.440%   $212.9466   $212.95   $212.95   $212.90  
  Purchase #3 $128.62   3.644%   $133.3069   $133.31   $133.30   $133.30  
  Purchase #4 $53.38   12.833%   $60.2303   $60.23   $60.25   $60.20  
  Purchase #5 $82.94   12.621%   $93.4079   $93.41   $93.40   $93.40  
  Purchase #6 $248.58   6.148%   $263.8627   $263.86   $263.85   $263.90  
  Purchase #7 $136.60   5.429%   $144.016   $144.02   $144.00   $144.00  
  7 purchase totals = $1,083.96       $1,153.8252   $1,153.83   $1,153.80   $1,153.80