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 $39.71   3.133%   $40.9541   $40.95   $40.95   $41.00  
  Purchase #2 $113.74   3.428%   $117.639   $117.64   $117.65   $117.60  
  Purchase #3 $157.48   3.762%   $163.4044   $163.40   $163.40   $163.40  
  Purchase #4 $231.55   11.699%   $258.639   $258.64   $258.65   $258.60  
  Purchase #5 $170.51   6.292%   $181.2385   $181.24   $181.25   $181.20  
  Purchase #6 $111.89   3.634%   $115.9561   $115.96   $115.95   $116.00  
  Purchase #7 $167.83   7.160%   $179.8466   $179.85   $179.85   $179.80  
  7 purchase totals = $992.71       $1,057.6777   $1,057.68   $1,057.70   $1,057.60