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 $117.41   4.760%   $122.9987   $123.00   $123.00   $123.00  
  Purchase #2 $249.40   7.794%   $268.8382   $268.84   $268.85   $268.80  
  Purchase #3 $103.39   9.657%   $113.3744   $113.37   $113.35   $113.40  
  Purchase #4 $245.76   7.152%   $263.3368   $263.34   $263.35   $263.30  
  Purchase #5 $87.78   4.238%   $91.5001   $91.50   $91.50   $91.50  
  Purchase #6 $187.27   13.358%   $212.2855   $212.29   $212.30   $212.30  
  Purchase #7 $179.90   11.360%   $200.3366   $200.34   $200.35   $200.30  
  7 purchase totals = $1,170.91       $1,272.6703   $1,272.68   $1,272.70   $1,272.60