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 $179.49   13.382%   $203.5094   $203.51   $203.50   $203.50  
  Purchase #2 $56.79   9.248%   $62.0419   $62.04   $62.05   $62.00  
  Purchase #3 $190.80   9.158%   $208.2735   $208.27   $208.25   $208.30  
  Purchase #4 $88.60   3.530%   $91.7276   $91.73   $91.75   $91.70  
  Purchase #5 $102.96   5.231%   $108.3458   $108.35   $108.35   $108.30  
  Purchase #6 $142.46   13.164%   $161.2134   $161.21   $161.20   $161.20  
  Purchase #7 $142.74   7.279%   $153.13   $153.13   $153.15   $153.10  
  7 purchase totals = $903.84       $988.2416   $988.24   $988.25   $988.10