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 $204.98   13.536%   $232.7261   $232.73   $232.75   $232.70  
  Purchase #2 $207.68   10.446%   $229.3743   $229.37   $229.35   $229.40  
  Purchase #3 $101.33   12.641%   $114.1391   $114.14   $114.15   $114.10  
  Purchase #4 $109.41   6.496%   $116.5173   $116.52   $116.50   $116.50  
  Purchase #5 $188.67   7.611%   $203.0297   $203.03   $203.05   $203.00  
  Purchase #6 $42.54   4.653%   $44.5194   $44.52   $44.50   $44.50  
  Purchase #7 $111.79   10.247%   $123.2451   $123.25   $123.25   $123.20  
  7 purchase totals = $966.40       $1,063.5510   $1,063.56   $1,063.55   $1,063.40