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 $85.75   7.344%   $92.0475   $92.05   $92.05   $92.00  
  Purchase #2 $152.95   3.125%   $157.7297   $157.73   $157.75   $157.70  
  Purchase #3 $238.57   4.722%   $249.8353   $249.84   $249.85   $249.80  
  Purchase #4 $226.72   8.215%   $245.345   $245.35   $245.35   $245.30  
  Purchase #5 $47.78   7.842%   $51.5269   $51.53   $51.55   $51.50  
  Purchase #6 $147.31   9.192%   $160.8507   $160.85   $160.85   $160.90  
  Purchase #7 $193.61   4.318%   $201.9701   $201.97   $201.95   $202.00  
  7 purchase totals = $1,092.69       $1,159.3052   $1,159.32   $1,159.35   $1,159.20