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 $24.97   6.352%   $26.5561   $26.56   $26.55   $26.60  
  Purchase #2 $141.70   13.335%   $160.5957   $160.60   $160.60   $160.60  
  Purchase #3 $218.56   3.115%   $225.3681   $225.37   $225.35   $225.40  
  Purchase #4 $52.52   3.511%   $54.364   $54.36   $54.35   $54.40  
  Purchase #5 $57.40   7.184%   $61.5236   $61.52   $61.50   $61.50  
  Purchase #6 $29.82   13.779%   $33.9289   $33.93   $33.95   $33.90  
  Purchase #7 $164.69   3.422%   $170.3257   $170.33   $170.35   $170.30  
  7 purchase totals = $689.66       $732.6621   $732.67   $732.65   $732.70