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 $93.62   13.260%   $106.034   $106.03   $106.05   $106.00  
  Purchase #2 $36.83   6.572%   $39.2505   $39.25   $39.25   $39.30  
  Purchase #3 $28.97   4.402%   $30.2453   $30.25   $30.25   $30.20  
  Purchase #4 $132.63   12.781%   $149.5814   $149.58   $149.60   $149.60  
  Purchase #5 $91.64   13.375%   $103.8969   $103.90   $103.90   $103.90  
  Purchase #6 $189.73   7.437%   $203.8402   $203.84   $203.85   $203.80  
  Purchase #7 $113.25   7.260%   $121.472   $121.47   $121.45   $121.50  
  7 purchase totals = $686.67       $754.3203   $754.32   $754.35   $754.30