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 $121.72   10.746%   $134.8   $134.80   $134.80   $134.80  
  Purchase #2 $184.59   4.733%   $193.3266   $193.33   $193.35   $193.30  
  Purchase #3 $148.91   11.137%   $165.4941   $165.49   $165.50   $165.50  
  Purchase #4 $51.96   7.158%   $55.6793   $55.68   $55.70   $55.70  
  Purchase #5 $192.80   10.648%   $213.3293   $213.33   $213.35   $213.30  
  Purchase #6 $68.96   3.281%   $71.2226   $71.22   $71.20   $71.20  
  Purchase #7 $243.49   12.464%   $273.8386   $273.84   $273.85   $273.80  
  7 purchase totals = $1,012.43       $1,107.6905   $1,107.69   $1,107.75   $1,107.60