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 $58.30   6.107%   $61.8604   $61.86   $61.85   $61.90  
  Purchase #2 $211.67   12.144%   $237.3752   $237.38   $237.40   $237.40  
  Purchase #3 $214.76   10.131%   $236.5173   $236.52   $236.50   $236.50  
  Purchase #4 $208.29   10.423%   $230.0001   $230.00   $230.00   $230.00  
  Purchase #5 $66.97   11.556%   $74.7091   $74.71   $74.70   $74.70  
  Purchase #6 $198.53   6.158%   $210.7555   $210.76   $210.75   $210.80  
  Purchase #7 $85.86   7.313%   $92.1389   $92.14   $92.15   $92.10  
  7 purchase totals = $1,044.38       $1,143.3565   $1,143.37   $1,143.35   $1,143.40