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 $65.95   11.117%   $73.2817   $73.28   $73.30   $73.30  
  Purchase #2 $158.55   7.334%   $170.1781   $170.18   $170.20   $170.20  
  Purchase #3 $212.78   4.178%   $221.6699   $221.67   $221.65   $221.70  
  Purchase #4 $206.80   8.342%   $224.0513   $224.05   $224.05   $224.10  
  Purchase #5 $201.93   11.475%   $225.1015   $225.10   $225.10   $225.10  
  Purchase #6 $246.69   12.761%   $278.1701   $278.17   $278.15   $278.20  
  Purchase #7 $165.43   8.864%   $180.0937   $180.09   $180.10   $180.10  
  7 purchase totals = $1,258.13       $1,372.5463   $1,372.54   $1,372.55   $1,372.70