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 $62.33   10.348%   $68.7799   $68.78   $68.80   $68.80  
  Purchase #2 $246.46   11.833%   $275.6236   $275.62   $275.60   $275.60  
  Purchase #3 $236.38   9.682%   $259.2663   $259.27   $259.25   $259.30  
  Purchase #4 $157.30   12.735%   $177.3322   $177.33   $177.35   $177.30  
  Purchase #5 $28.29   7.809%   $30.4992   $30.50   $30.50   $30.50  
  Purchase #6 $155.48   10.429%   $171.695   $171.70   $171.70   $171.70  
  Purchase #7 $71.52   5.429%   $75.4028   $75.40   $75.40   $75.40  
  7 purchase totals = $957.76       $1,058.5990   $1,058.60   $1,058.60   $1,058.60