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 $204.84   12.819%   $231.0984   $231.10   $231.10   $231.10  
  Purchase #2 $58.40   10.141%   $64.3223   $64.32   $64.30   $64.30  
  Purchase #3 $106.40   7.268%   $114.1332   $114.13   $114.15   $114.10  
  Purchase #4 $110.49   7.391%   $118.6563   $118.66   $118.65   $118.70  
  Purchase #5 $88.45   7.619%   $95.189   $95.19   $95.20   $95.20  
  Purchase #6 $135.55   7.392%   $145.5699   $145.57   $145.55   $145.60  
  Purchase #7 $191.27   3.129%   $197.2548   $197.25   $197.25   $197.30  
  7 purchase totals = $895.40       $966.2239   $966.22   $966.20   $966.30