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 $246.87   11.741%   $275.855   $275.86   $275.85   $275.90  
  Purchase #2 $49.85   6.216%   $52.9487   $52.95   $52.95   $52.90  
  Purchase #3 $64.99   4.648%   $68.0107   $68.01   $68.00   $68.00  
  Purchase #4 $181.33   4.498%   $189.4862   $189.49   $189.50   $189.50  
  Purchase #5 $110.71   4.418%   $115.6012   $115.60   $115.60   $115.60  
  Purchase #6 $187.49   10.236%   $206.6815   $206.68   $206.70   $206.70  
  Purchase #7 $211.86   10.467%   $234.0354   $234.04   $234.05   $234.00  
  7 purchase totals = $1,053.10       $1,142.6187   $1,142.63   $1,142.65   $1,142.60