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 $215.85   13.158%   $244.2515   $244.25   $244.25   $244.30  
  Purchase #2 $135.41   10.354%   $149.4304   $149.43   $149.45   $149.40  
  Purchase #3 $97.63   8.595%   $106.0213   $106.02   $106.00   $106.00  
  Purchase #4 $43.80   13.560%   $49.7393   $49.74   $49.75   $49.70  
  Purchase #5 $31.55   11.180%   $35.0773   $35.08   $35.10   $35.10  
  Purchase #6 $241.33   9.413%   $264.0464   $264.05   $264.05   $264.00  
  Purchase #7 $123.93   7.539%   $133.2731   $133.27   $133.25   $133.30  
  7 purchase totals = $889.50       $981.8393   $981.84   $981.85   $981.80