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 $230.49   7.426%   $247.6062   $247.61   $247.60   $247.60  
  Purchase #2 $59.45   11.332%   $66.1869   $66.19   $66.20   $66.20  
  Purchase #3 $76.71   9.261%   $83.8141   $83.81   $83.80   $83.80  
  Purchase #4 $123.76   7.386%   $132.9009   $132.90   $132.90   $132.90  
  Purchase #5 $227.33   7.434%   $244.2297   $244.23   $244.25   $244.20  
  Purchase #6 $134.58   4.392%   $140.4908   $140.49   $140.50   $140.50  
  Purchase #7 $88.66   9.232%   $96.8451   $96.85   $96.85   $96.80  
  7 purchase totals = $940.98       $1,012.0737   $1,012.08   $1,012.10   $1,012.00