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 $76.87   5.729%   $81.2739   $81.27   $81.25   $81.30  
  Purchase #2 $113.57   7.559%   $122.1548   $122.15   $122.15   $122.20  
  Purchase #3 $183.44   9.690%   $201.2153   $201.22   $201.20   $201.20  
  Purchase #4 $244.91   12.823%   $276.3148   $276.31   $276.30   $276.30  
  Purchase #5 $62.49   3.787%   $64.8565   $64.86   $64.85   $64.90  
  Purchase #6 $246.52   11.629%   $275.1878   $275.19   $275.20   $275.20  
  Purchase #7 $70.62   13.572%   $80.2045   $80.20   $80.20   $80.20  
  7 purchase totals = $998.42       $1,101.2076   $1,101.20   $1,101.15   $1,101.30