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 $165.59   12.292%   $185.9443   $185.94   $185.95   $185.90  
  Purchase #2 $146.68   4.282%   $152.9608   $152.96   $152.95   $153.00  
  Purchase #3 $45.76   11.557%   $51.0485   $51.05   $51.05   $51.00  
  Purchase #4 $67.25   10.309%   $74.1828   $74.18   $74.20   $74.20  
  Purchase #5 $229.56   5.800%   $242.8745   $242.87   $242.85   $242.90  
  Purchase #6 $183.54   12.560%   $206.5926   $206.59   $206.60   $206.60  
  Purchase #7 $211.91   11.247%   $235.7435   $235.74   $235.75   $235.70  
  7 purchase totals = $1,050.29       $1,149.3470   $1,149.33   $1,149.35   $1,149.30