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 $240.74   7.279%   $258.2635   $258.26   $258.25   $258.30  
  Purchase #2 $64.63   5.238%   $68.0153   $68.02   $68.00   $68.00  
  Purchase #3 $225.55   8.717%   $245.2112   $245.21   $245.20   $245.20  
  Purchase #4 $61.46   10.626%   $67.9907   $67.99   $68.00   $68.00  
  Purchase #5 $93.72   3.746%   $97.2308   $97.23   $97.25   $97.20  
  Purchase #6 $212.37   6.401%   $225.9638   $225.96   $225.95   $226.00  
  Purchase #7 $59.63   5.799%   $63.0879   $63.09   $63.10   $63.10  
  7 purchase totals = $958.10       $1,025.7632   $1,025.76   $1,025.75   $1,025.80