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 $247.96   9.836%   $272.3493   $272.35   $272.35   $272.30  
  Purchase #2 $174.53   11.399%   $194.4247   $194.42   $194.40   $194.40  
  Purchase #3 $194.81   4.822%   $204.2037   $204.20   $204.20   $204.20  
  Purchase #4 $197.68   9.544%   $216.5466   $216.55   $216.55   $216.50  
  Purchase #5 $63.78   6.755%   $68.0883   $68.09   $68.10   $68.10  
  Purchase #6 $98.74   5.196%   $103.8705   $103.87   $103.85   $103.90  
  Purchase #7 $197.90   3.649%   $205.1214   $205.12   $205.10   $205.10  
  7 purchase totals = $1,175.40       $1,264.6045   $1,264.60   $1,264.55   $1,264.50