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 $54.65   7.609%   $58.8083   $58.81   $58.80   $58.80  
  Purchase #2 $183.60   6.214%   $195.0089   $195.01   $195.00   $195.00  
  Purchase #3 $229.62   11.850%   $256.83   $256.83   $256.85   $256.80  
  Purchase #4 $247.48   11.271%   $275.3735   $275.37   $275.35   $275.40  
  Purchase #5 $130.66   7.385%   $140.3092   $140.31   $140.30   $140.30  
  Purchase #6 $211.34   5.198%   $222.3255   $222.33   $222.35   $222.30  
  Purchase #7 $51.94   8.785%   $56.5029   $56.50   $56.50   $56.50  
  7 purchase totals = $1,109.29       $1,205.1583   $1,205.16   $1,205.15   $1,205.10