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 $55.37   10.556%   $61.2149   $61.21   $61.20   $61.20  
  Purchase #2 $147.35   7.121%   $157.8428   $157.84   $157.85   $157.80  
  Purchase #3 $61.63   7.345%   $66.1567   $66.16   $66.15   $66.20  
  Purchase #4 $106.58   3.525%   $110.3369   $110.34   $110.35   $110.30  
  Purchase #5 $216.93   13.152%   $245.4606   $245.46   $245.45   $245.50  
  Purchase #6 $156.39   9.739%   $171.6208   $171.62   $171.60   $171.60  
  Purchase #7 $181.40   13.328%   $205.577   $205.58   $205.60   $205.60  
  7 purchase totals = $925.65       $1,018.2097   $1,018.21   $1,018.20   $1,018.20