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 $52.80   11.658%   $58.9554   $58.96   $58.95   $59.00  
  Purchase #2 $128.64   3.254%   $132.8259   $132.83   $132.85   $132.80  
  Purchase #3 $49.73   5.745%   $52.587   $52.59   $52.60   $52.60  
  Purchase #4 $5.37   4.135%   $5.592   $5.59   $5.60   $5.60  
  Purchase #5 $74.75   8.287%   $80.9445   $80.94   $80.95   $80.90  
  Purchase #6 $13.46   6.840%   $14.3807   $14.38   $14.40   $14.40  
  Purchase #7 $180.84   11.424%   $201.4992   $201.50   $201.50   $201.50  
  7 purchase totals = $505.59       $546.7847   $546.79   $546.85   $546.80