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 $226.57   4.290%   $236.2899   $236.29   $236.30   $236.30  
  Purchase #2 $67.96   4.226%   $70.832   $70.83   $70.85   $70.80  
  Purchase #3 $43.95   4.372%   $45.8715   $45.87   $45.85   $45.90  
  Purchase #4 $194.61   4.734%   $203.8228   $203.82   $203.80   $203.80  
  Purchase #5 $101.87   9.492%   $111.5395   $111.54   $111.55   $111.50  
  Purchase #6 $83.94   11.238%   $93.3732   $93.37   $93.35   $93.40  
  Purchase #7 $198.75   6.657%   $211.9808   $211.98   $212.00   $212.00  
  7 purchase totals = $917.65       $973.7097   $973.70   $973.70   $973.70