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 $61.90   3.612%   $64.1358   $64.14   $64.15   $64.10  
  Purchase #2 $85.60   11.796%   $95.6974   $95.70   $95.70   $95.70  
  Purchase #3 $136.35   12.840%   $153.8573   $153.86   $153.85   $153.90  
  Purchase #4 $75.85   12.855%   $85.6005   $85.60   $85.60   $85.60  
  Purchase #5 $132.54   13.839%   $150.8822   $150.88   $150.90   $150.90  
  Purchase #6 $202.52   4.507%   $211.6476   $211.65   $211.65   $211.60  
  Purchase #7 $76.60   10.537%   $84.6713   $84.67   $84.65   $84.70  
  7 purchase totals = $771.36       $846.4921   $846.50   $846.50   $846.50