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 $38.87   7.409%   $41.7499   $41.75   $41.75   $41.70  
  Purchase #2 $153.32   8.199%   $165.8907   $165.89   $165.90   $165.90  
  Purchase #3 $215.93   6.279%   $229.4882   $229.49   $229.50   $229.50  
  Purchase #4 $146.94   10.630%   $162.5597   $162.56   $162.55   $162.60  
  Purchase #5 $99.73   3.104%   $102.8256   $102.83   $102.85   $102.80  
  Purchase #6 $106.79   12.707%   $120.3598   $120.36   $120.35   $120.40  
  Purchase #7 $184.38   10.323%   $203.4135   $203.41   $203.40   $203.40  
  7 purchase totals = $945.96       $1,026.2874   $1,026.29   $1,026.30   $1,026.30