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 $54.34   12.367%   $61.0602   $61.06   $61.05   $61.10  
  Purchase #2 $245.87   11.417%   $273.941   $273.94   $273.95   $273.90  
  Purchase #3 $203.92   6.508%   $217.1911   $217.19   $217.20   $217.20  
  Purchase #4 $23.53   8.113%   $25.439   $25.44   $25.45   $25.40  
  Purchase #5 $224.39   7.700%   $241.668   $241.67   $241.65   $241.70  
  Purchase #6 $154.73   6.511%   $164.8045   $164.80   $164.80   $164.80  
  Purchase #7 $155.39   5.735%   $164.3016   $164.30   $164.30   $164.30  
  7 purchase totals = $1,062.17       $1,148.4054   $1,148.40   $1,148.40   $1,148.40