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 $73.94   5.408%   $77.9387   $77.94   $77.95   $77.90  
  Purchase #2 $172.62   12.523%   $194.2372   $194.24   $194.25   $194.20  
  Purchase #3 $242.95   5.305%   $255.8385   $255.84   $255.85   $255.80  
  Purchase #4 $178.39   13.430%   $202.3478   $202.35   $202.35   $202.30  
  Purchase #5 $54.33   7.367%   $58.3325   $58.33   $58.35   $58.30  
  Purchase #6 $156.90   13.400%   $177.9246   $177.92   $177.90   $177.90  
  Purchase #7 $180.63   13.506%   $205.0259   $205.03   $205.05   $205.00  
  7 purchase totals = $1,059.76       $1,171.6452   $1,171.65   $1,171.70   $1,171.40