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 $196.94   10.683%   $217.9791   $217.98   $218.00   $218.00  
  Purchase #2 $237.75   13.651%   $270.2053   $270.21   $270.20   $270.20  
  Purchase #3 $113.98   5.514%   $120.2649   $120.26   $120.25   $120.30  
  Purchase #4 $217.60   11.658%   $242.9678   $242.97   $242.95   $243.00  
  Purchase #5 $238.55   5.572%   $251.842   $251.84   $251.85   $251.80  
  Purchase #6 $27.48   7.170%   $29.4503   $29.45   $29.45   $29.50  
  Purchase #7 $77.31   7.103%   $82.8013   $82.80   $82.80   $82.80  
  7 purchase totals = $1,109.61       $1,215.5107   $1,215.51   $1,215.50   $1,215.60