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 $165.82   12.223%   $186.0882   $186.09   $186.10   $186.10  
  Purchase #2 $189.73   7.867%   $204.6561   $204.66   $204.65   $204.70  
  Purchase #3 $227.83   4.199%   $237.3966   $237.40   $237.40   $237.40  
  Purchase #4 $93.25   4.782%   $97.7092   $97.71   $97.70   $97.70  
  Purchase #5 $179.92   13.846%   $204.8317   $204.83   $204.85   $204.80  
  Purchase #6 $54.57   3.657%   $56.5656   $56.57   $56.55   $56.60  
  Purchase #7 $32.90   9.504%   $36.0268   $36.03   $36.05   $36.00  
  7 purchase totals = $944.02       $1,023.2742   $1,023.29   $1,023.30   $1,023.30