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 $46.60   4.573%   $48.731   $48.73   $48.75   $48.70  
  Purchase #2 $213.85   10.779%   $236.9009   $236.90   $236.90   $236.90  
  Purchase #3 $154.87   13.118%   $175.1858   $175.19   $175.20   $175.20  
  Purchase #4 $46.98   3.396%   $48.5754   $48.58   $48.60   $48.60  
  Purchase #5 $80.35   13.827%   $91.46   $91.46   $91.45   $91.50  
  Purchase #6 $225.33   8.515%   $244.5168   $244.52   $244.50   $244.50  
  Purchase #7 $174.48   6.752%   $186.2609   $186.26   $186.25   $186.30  
  7 purchase totals = $942.46       $1,031.6308   $1,031.64   $1,031.65   $1,031.70