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 $58.25   5.772%   $61.6122   $61.61   $61.60   $61.60  
  Purchase #2 $37.52   5.837%   $39.71   $39.71   $39.70   $39.70  
  Purchase #3 $105.88   4.639%   $110.7918   $110.79   $110.80   $110.80  
  Purchase #4 $223.75   11.814%   $250.1838   $250.18   $250.20   $250.20  
  Purchase #5 $234.94   12.551%   $264.4273   $264.43   $264.45   $264.40  
  Purchase #6 $6.45   3.364%   $6.667   $6.67   $6.65   $6.70  
  Purchase #7 $167.91   11.754%   $187.6461   $187.65   $187.65   $187.60  
  7 purchase totals = $834.70       $921.0382   $921.04   $921.05   $921.00