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 $231.52   12.799%   $261.1522   $261.15   $261.15   $261.20  
  Purchase #2 $237.39   9.435%   $259.7877   $259.79   $259.80   $259.80  
  Purchase #3 $121.85   13.623%   $138.4496   $138.45   $138.45   $138.40  
  Purchase #4 $234.44   9.434%   $256.5571   $256.56   $256.55   $256.60  
  Purchase #5 $234.28   12.109%   $262.649   $262.65   $262.65   $262.60  
  Purchase #6 $97.37   9.200%   $106.328   $106.33   $106.35   $106.30  
  Purchase #7 $65.49   6.362%   $69.6565   $69.66   $69.65   $69.70  
  7 purchase totals = $1,222.34       $1,354.5801   $1,354.59   $1,354.60   $1,354.60