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 $77.59   11.790%   $86.7379   $86.74   $86.75   $86.70  
  Purchase #2 $83.41   5.447%   $87.9533   $87.95   $87.95   $88.00  
  Purchase #3 $91.80   5.183%   $96.558   $96.56   $96.55   $96.60  
  Purchase #4 $204.29   7.658%   $219.9345   $219.93   $219.95   $219.90  
  Purchase #5 $130.40   13.543%   $148.0601   $148.06   $148.05   $148.10  
  Purchase #6 $169.32   7.770%   $182.4762   $182.48   $182.50   $182.50  
  Purchase #7 $211.44   13.486%   $239.9548   $239.95   $239.95   $240.00  
  7 purchase totals = $968.25       $1,061.6748   $1,061.67   $1,061.70   $1,061.80