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 $70.81   7.822%   $76.3488   $76.35   $76.35   $76.30  
  Purchase #2 $163.29   10.744%   $180.8339   $180.83   $180.85   $180.80  
  Purchase #3 $221.94   10.641%   $245.5566   $245.56   $245.55   $245.60  
  Purchase #4 $222.44   3.158%   $229.4647   $229.46   $229.45   $229.50  
  Purchase #5 $206.93   11.669%   $231.0767   $231.08   $231.10   $231.10  
  Purchase #6 $89.26   9.528%   $97.7647   $97.76   $97.75   $97.80  
  Purchase #7 $109.76   5.823%   $116.1513   $116.15   $116.15   $116.20  
  7 purchase totals = $1,084.43       $1,177.1967   $1,177.19   $1,177.20   $1,177.30