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 $192.65   13.678%   $219.0007   $219.00   $219.00   $219.00  
  Purchase #2 $41.28   11.305%   $45.9467   $45.95   $45.95   $45.90  
  Purchase #3 $109.54   11.255%   $121.8687   $121.87   $121.85   $121.90  
  Purchase #4 $41.28   12.190%   $46.312   $46.31   $46.30   $46.30  
  Purchase #5 $187.89   11.687%   $209.8487   $209.85   $209.85   $209.80  
  Purchase #6 $218.43   6.405%   $232.4204   $232.42   $232.40   $232.40  
  Purchase #7 $84.67   13.284%   $95.9176   $95.92   $95.90   $95.90  
  7 purchase totals = $875.74       $971.3148   $971.32   $971.25   $971.20