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 $236.93   13.179%   $268.155   $268.16   $268.15   $268.20  
  Purchase #2 $164.47   7.347%   $176.5536   $176.55   $176.55   $176.60  
  Purchase #3 $28.64   13.647%   $32.5485   $32.55   $32.55   $32.50  
  Purchase #4 $205.64   13.815%   $234.0492   $234.05   $234.05   $234.00  
  Purchase #5 $146.52   4.457%   $153.0504   $153.05   $153.05   $153.10  
  Purchase #6 $20.67   8.321%   $22.39   $22.39   $22.40   $22.40  
  Purchase #7 $183.28   10.279%   $202.1194   $202.12   $202.10   $202.10  
  7 purchase totals = $986.15       $1,088.8661   $1,088.87   $1,088.85   $1,088.90