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 $152.67   9.286%   $166.8469   $166.85   $166.85   $166.80  
  Purchase #2 $27.28   7.357%   $29.287   $29.29   $29.30   $29.30  
  Purchase #3 $101.82   5.273%   $107.189   $107.19   $107.20   $107.20  
  Purchase #4 $65.55   4.809%   $68.7023   $68.70   $68.70   $68.70  
  Purchase #5 $53.62   11.820%   $59.9579   $59.96   $59.95   $60.00  
  Purchase #6 $187.90   6.391%   $199.9087   $199.91   $199.90   $199.90  
  Purchase #7 $212.34   3.555%   $219.8887   $219.89   $219.90   $219.90  
  7 purchase totals = $801.18       $851.7805   $851.79   $851.80   $851.80