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 $87.48   4.644%   $91.5426   $91.54   $91.55   $91.50  
  Purchase #2 $29.98   12.413%   $33.7014   $33.70   $33.70   $33.70  
  Purchase #3 $187.81   11.442%   $209.2992   $209.30   $209.30   $209.30  
  Purchase #4 $124.26   7.514%   $133.5969   $133.60   $133.60   $133.60  
  Purchase #5 $51.74   6.409%   $55.056   $55.06   $55.05   $55.10  
  Purchase #6 $243.97   5.862%   $258.2715   $258.27   $258.25   $258.30  
  Purchase #7 $214.54   5.839%   $227.067   $227.07   $227.05   $227.10  
  7 purchase totals = $939.78       $1,008.5346   $1,008.54   $1,008.50   $1,008.60