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 $48.57   13.776%   $55.261   $55.26   $55.25   $55.30  
  Purchase #2 $151.29   11.238%   $168.292   $168.29   $168.30   $168.30  
  Purchase #3 $189.98   8.411%   $205.9592   $205.96   $205.95   $206.00  
  Purchase #4 $60.59   9.135%   $66.1249   $66.12   $66.10   $66.10  
  Purchase #5 $201.53   3.391%   $208.3639   $208.36   $208.35   $208.40  
  Purchase #6 $192.53   6.841%   $205.701   $205.70   $205.70   $205.70  
  Purchase #7 $118.38   5.645%   $125.0626   $125.06   $125.05   $125.10  
  7 purchase totals = $962.87       $1,034.7646   $1,034.75   $1,034.70   $1,034.90