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 $48.84   7.631%   $52.567   $52.57   $52.55   $52.60  
  Purchase #2 $204.95   13.664%   $232.9544   $232.95   $232.95   $233.00  
  Purchase #3 $75.25   6.684%   $80.2797   $80.28   $80.30   $80.30  
  Purchase #4 $188.69   8.572%   $204.8645   $204.86   $204.85   $204.90  
  Purchase #5 $66.35   4.569%   $69.3815   $69.38   $69.40   $69.40  
  Purchase #6 $147.98   8.711%   $160.8705   $160.87   $160.85   $160.90  
  Purchase #7 $143.39   3.425%   $148.3011   $148.30   $148.30   $148.30  
  7 purchase totals = $875.45       $949.2187   $949.21   $949.20   $949.40