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 $49.81   8.626%   $54.1066   $54.11   $54.10   $54.10  
  Purchase #2 $75.82   9.505%   $83.0267   $83.03   $83.05   $83.00  
  Purchase #3 $29.62   7.710%   $31.9037   $31.90   $31.90   $31.90  
  Purchase #4 $240.47   13.588%   $273.1451   $273.15   $273.15   $273.10  
  Purchase #5 $184.78   13.802%   $210.2833   $210.28   $210.30   $210.30  
  Purchase #6 $88.30   6.457%   $94.0015   $94.00   $94.00   $94.00  
  Purchase #7 $203.91   5.222%   $214.5582   $214.56   $214.55   $214.60  
  7 purchase totals = $872.71       $961.0251   $961.03   $961.05   $961.00