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 $61.79   11.690%   $69.0133   $69.01   $69.00   $69.00  
  Purchase #2 $122.80   3.740%   $127.3927   $127.39   $127.40   $127.40  
  Purchase #3 $148.67   11.286%   $165.4489   $165.45   $165.45   $165.40  
  Purchase #4 $231.94   12.870%   $261.7907   $261.79   $261.80   $261.80  
  Purchase #5 $59.61   8.236%   $64.5195   $64.52   $64.50   $64.50  
  Purchase #6 $199.39   5.672%   $210.6994   $210.70   $210.70   $210.70  
  Purchase #7 $232.65   11.765%   $260.0213   $260.02   $260.00   $260.00  
  7 purchase totals = $1,056.85       $1,158.8858   $1,158.88   $1,158.85   $1,158.80