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 $211.66   10.564%   $234.0198   $234.02   $234.00   $234.00  
  Purchase #2 $188.56   6.666%   $201.1294   $201.13   $201.15   $201.10  
  Purchase #3 $61.86   13.333%   $70.1078   $70.11   $70.10   $70.10  
  Purchase #4 $249.92   7.372%   $268.3441   $268.34   $268.35   $268.30  
  Purchase #5 $163.70   5.317%   $172.4039   $172.40   $172.40   $172.40  
  Purchase #6 $194.62   11.652%   $217.2971   $217.30   $217.30   $217.30  
  Purchase #7 $129.98   6.717%   $138.7108   $138.71   $138.70   $138.70  
  7 purchase totals = $1,200.30       $1,302.0129   $1,302.01   $1,302.00   $1,301.90