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 $105.39   9.761%   $115.6771   $115.68   $115.70   $115.70  
  Purchase #2 $112.96   7.115%   $120.9971   $121.00   $121.00   $121.00  
  Purchase #3 $109.49   6.633%   $116.7525   $116.75   $116.75   $116.80  
  Purchase #4 $229.42   5.193%   $241.3338   $241.33   $241.35   $241.30  
  Purchase #5 $248.33   13.365%   $281.5193   $281.52   $281.50   $281.50  
  Purchase #6 $104.91   12.417%   $117.9367   $117.94   $117.95   $117.90  
  Purchase #7 $82.93   6.514%   $88.3321   $88.33   $88.35   $88.30  
  7 purchase totals = $993.43       $1,082.5486   $1,082.55   $1,082.60   $1,082.50