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 $60.96   11.607%   $68.0356   $68.04   $68.05   $68.00  
  Purchase #2 $28.91   13.672%   $32.8626   $32.86   $32.85   $32.90  
  Purchase #3 $226.70   4.424%   $236.7292   $236.73   $236.75   $236.70  
  Purchase #4 $26.41   13.319%   $29.9275   $29.93   $29.95   $29.90  
  Purchase #5 $142.76   9.857%   $156.8319   $156.83   $156.85   $156.80  
  Purchase #6 $135.80   4.453%   $141.8472   $141.85   $141.85   $141.80  
  Purchase #7 $49.72   11.317%   $55.3468   $55.35   $55.35   $55.30  
  7 purchase totals = $671.26       $721.5808   $721.59   $721.65   $721.40