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 $54.55   13.272%   $61.7899   $61.79   $61.80   $61.80  
  Purchase #2 $161.92   9.215%   $176.8409   $176.84   $176.85   $176.80  
  Purchase #3 $197.49   5.864%   $209.0708   $209.07   $209.05   $209.10  
  Purchase #4 $159.51   9.793%   $175.1308   $175.13   $175.15   $175.10  
  Purchase #5 $186.35   9.846%   $204.698   $204.70   $204.70   $204.70  
  Purchase #6 $249.78   13.472%   $283.4304   $283.43   $283.45   $283.40  
  Purchase #7 $198.37   3.265%   $204.8468   $204.85   $204.85   $204.80  
  7 purchase totals = $1,207.97       $1,315.8076   $1,315.81   $1,315.85   $1,315.70