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 $67.79   12.756%   $76.4373   $76.44   $76.45   $76.40  
  Purchase #2 $166.37   3.811%   $172.7104   $172.71   $172.70   $172.70  
  Purchase #3 $148.80   4.736%   $155.8472   $155.85   $155.85   $155.80  
  Purchase #4 $104.97   12.568%   $118.1626   $118.16   $118.15   $118.20  
  Purchase #5 $24.56   9.281%   $26.8394   $26.84   $26.85   $26.80  
  Purchase #6 $163.45   11.745%   $182.6472   $182.65   $182.65   $182.60  
  Purchase #7 $208.78   5.417%   $220.0896   $220.09   $220.10   $220.10  
  7 purchase totals = $884.72       $952.7337   $952.74   $952.75   $952.60