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 $55.91   9.133%   $61.0163   $61.02   $61.00   $61.00  
  Purchase #2 $66.56   11.701%   $74.3482   $74.35   $74.35   $74.30  
  Purchase #3 $23.56   9.482%   $25.794   $25.79   $25.80   $25.80  
  Purchase #4 $146.30   3.265%   $151.0767   $151.08   $151.10   $151.10  
  Purchase #5 $216.87   6.814%   $231.6475   $231.65   $231.65   $231.60  
  Purchase #6 $132.81   4.291%   $138.5089   $138.51   $138.50   $138.50  
  Purchase #7 $108.74   6.498%   $115.8059   $115.81   $115.80   $115.80  
  7 purchase totals = $750.75       $798.1975   $798.21   $798.20   $798.10