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 $91.44   4.374%   $95.4396   $95.44   $95.45   $95.40  
  Purchase #2 $44.55   7.229%   $47.7705   $47.77   $47.75   $47.80  
  Purchase #3 $39.60   5.222%   $41.6679   $41.67   $41.65   $41.70  
  Purchase #4 $245.43   5.846%   $259.7778   $259.78   $259.80   $259.80  
  Purchase #5 $54.85   11.391%   $61.098   $61.10   $61.10   $61.10  
  Purchase #6 $116.74   10.666%   $129.1915   $129.19   $129.20   $129.20  
  Purchase #7 $203.33   10.800%   $225.2896   $225.29   $225.30   $225.30  
  7 purchase totals = $795.94       $860.2349   $860.24   $860.25   $860.30