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 $74.32   3.413%   $76.8565   $76.86   $76.85   $76.90  
  Purchase #2 $211.96   6.577%   $225.9006   $225.90   $225.90   $225.90  
  Purchase #3 $73.28   8.765%   $79.703   $79.70   $79.70   $79.70  
  Purchase #4 $232.26   10.446%   $256.5219   $256.52   $256.50   $256.50  
  Purchase #5 $214.74   13.651%   $244.0542   $244.05   $244.05   $244.10  
  Purchase #6 $108.91   9.490%   $119.2456   $119.25   $119.25   $119.20  
  Purchase #7 $29.97   8.340%   $32.4695   $32.47   $32.45   $32.50  
  7 purchase totals = $945.44       $1,034.7513   $1,034.75   $1,034.70   $1,034.80