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 $225.71   9.373%   $246.8658   $246.87   $246.85   $246.90  
  Purchase #2 $45.88   7.514%   $49.3274   $49.33   $49.35   $49.30  
  Purchase #3 $62.57   9.831%   $68.7213   $68.72   $68.70   $68.70  
  Purchase #4 $179.46   9.874%   $197.1799   $197.18   $197.20   $197.20  
  Purchase #5 $159.75   12.353%   $179.4839   $179.48   $179.50   $179.50  
  Purchase #6 $165.93   6.381%   $176.518   $176.52   $176.50   $176.50  
  Purchase #7 $89.36   13.811%   $101.7015   $101.70   $101.70   $101.70  
  7 purchase totals = $928.66       $1,019.7978   $1,019.80   $1,019.80   $1,019.80