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 $227.64   9.161%   $248.4941   $248.49   $248.50   $248.50  
  Purchase #2 $130.89   12.794%   $147.6361   $147.64   $147.65   $147.60  
  Purchase #3 $52.79   5.219%   $55.5451   $55.55   $55.55   $55.50  
  Purchase #4 $154.33   7.287%   $165.576   $165.58   $165.60   $165.60  
  Purchase #5 $141.40   5.579%   $149.2887   $149.29   $149.30   $149.30  
  Purchase #6 $234.95   10.372%   $259.319   $259.32   $259.30   $259.30  
  Purchase #7 $52.43   12.220%   $58.8369   $58.84   $58.85   $58.80  
  7 purchase totals = $994.43       $1,084.6959   $1,084.71   $1,084.75   $1,084.60