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 $57.45   8.323%   $62.2316   $62.23   $62.25   $62.20  
  Purchase #2 $204.71   6.135%   $217.269   $217.27   $217.25   $217.30  
  Purchase #3 $233.99   7.677%   $251.9534   $251.95   $251.95   $252.00  
  Purchase #4 $110.31   10.480%   $121.8705   $121.87   $121.85   $121.90  
  Purchase #5 $187.59   8.563%   $203.6533   $203.65   $203.65   $203.70  
  Purchase #6 $130.61   13.818%   $148.6577   $148.66   $148.65   $148.70  
  Purchase #7 $248.34   4.191%   $258.7479   $258.75   $258.75   $258.70  
  7 purchase totals = $1,173.00       $1,264.3834   $1,264.38   $1,264.35   $1,264.50