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 $192.55   13.374%   $218.3016   $218.30   $218.30   $218.30  
  Purchase #2 $62.52   4.835%   $65.5428   $65.54   $65.55   $65.50  
  Purchase #3 $227.35   6.383%   $241.8618   $241.86   $241.85   $241.90  
  Purchase #4 $9.73   5.284%   $10.2441   $10.24   $10.25   $10.20  
  Purchase #5 $168.83   13.197%   $191.1105   $191.11   $191.10   $191.10  
  Purchase #6 $212.75   5.288%   $224.0002   $224.00   $224.00   $224.00  
  Purchase #7 $157.48   6.165%   $167.1886   $167.19   $167.20   $167.20  
  7 purchase totals = $1,031.21       $1,118.2496   $1,118.24   $1,118.25   $1,118.20