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 $243.62   7.337%   $261.4944   $261.49   $261.50   $261.50  
  Purchase #2 $177.41   13.608%   $201.552   $201.55   $201.55   $201.60  
  Purchase #3 $93.48   11.482%   $104.2134   $104.21   $104.20   $104.20  
  Purchase #4 $182.60   10.313%   $201.4315   $201.43   $201.45   $201.40  
  Purchase #5 $134.74   8.644%   $146.3869   $146.39   $146.40   $146.40  
  Purchase #6 $97.95   8.300%   $106.0799   $106.08   $106.10   $106.10  
  Purchase #7 $216.26   8.511%   $234.6659   $234.67   $234.65   $234.70  
  7 purchase totals = $1,146.06       $1,255.8240   $1,255.82   $1,255.85   $1,255.90