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 $53.32   13.326%   $60.4254   $60.43   $60.45   $60.40  
  Purchase #2 $187.94   9.583%   $205.9503   $205.95   $205.95   $206.00  
  Purchase #3 $107.37   13.141%   $121.4795   $121.48   $121.50   $121.50  
  Purchase #4 $75.26   9.170%   $82.1613   $82.16   $82.15   $82.20  
  Purchase #5 $151.72   12.251%   $170.3072   $170.31   $170.30   $170.30  
  Purchase #6 $181.61   13.216%   $205.6116   $205.61   $205.60   $205.60  
  Purchase #7 $217.56   13.553%   $247.0459   $247.05   $247.05   $247.00  
  7 purchase totals = $974.78       $1,092.9812   $1,092.99   $1,093.00   $1,093.00