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 $118.89   12.607%   $133.8785   $133.88   $133.90   $133.90  
  Purchase #2 $191.91   12.558%   $216.0101   $216.01   $216.00   $216.00  
  Purchase #3 $100.36   6.175%   $106.5572   $106.56   $106.55   $106.60  
  Purchase #4 $236.50   4.661%   $247.5233   $247.52   $247.50   $247.50  
  Purchase #5 $169.73   8.516%   $184.1842   $184.18   $184.20   $184.20  
  Purchase #6 $103.49   11.787%   $115.6884   $115.69   $115.70   $115.70  
  Purchase #7 $19.88   4.770%   $20.8283   $20.83   $20.85   $20.80  
  7 purchase totals = $940.76       $1,024.6700   $1,024.67   $1,024.70   $1,024.70