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 $37.94   6.217%   $40.2987   $40.30   $40.30   $40.30  
  Purchase #2 $198.74   5.710%   $210.0881   $210.09   $210.10   $210.10  
  Purchase #3 $232.85   13.516%   $264.322   $264.32   $264.30   $264.30  
  Purchase #4 $73.92   4.378%   $77.1562   $77.16   $77.15   $77.20  
  Purchase #5 $63.46   4.242%   $66.152   $66.15   $66.15   $66.20  
  Purchase #6 $67.84   6.421%   $72.196   $72.20   $72.20   $72.20  
  Purchase #7 $11.46   4.334%   $11.9567   $11.96   $11.95   $12.00  
  7 purchase totals = $686.21       $742.1697   $742.18   $742.15   $742.30