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 $248.54   11.722%   $277.6739   $277.67   $277.65   $277.70  
  Purchase #2 $59.67   9.852%   $65.5487   $65.55   $65.55   $65.50  
  Purchase #3 $31.92   7.172%   $34.2093   $34.21   $34.20   $34.20  
  Purchase #4 $210.31   7.655%   $226.4092   $226.41   $226.40   $226.40  
  Purchase #5 $147.73   9.212%   $161.3389   $161.34   $161.35   $161.30  
  Purchase #6 $167.92   8.632%   $182.4149   $182.41   $182.40   $182.40  
  Purchase #7 $25.40   9.809%   $27.8915   $27.89   $27.90   $27.90  
  7 purchase totals = $891.49       $975.4864   $975.48   $975.45   $975.40