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 $88.36   10.791%   $97.8949   $97.89   $97.90   $97.90  
  Purchase #2 $228.77   4.718%   $239.5634   $239.56   $239.55   $239.60  
  Purchase #3 $193.46   4.824%   $202.7925   $202.79   $202.80   $202.80  
  Purchase #4 $164.78   6.775%   $175.9438   $175.94   $175.95   $175.90  
  Purchase #5 $19.36   10.227%   $21.3399   $21.34   $21.35   $21.30  
  Purchase #6 $240.59   8.159%   $260.2197   $260.22   $260.20   $260.20  
  Purchase #7 $31.48   11.322%   $35.0442   $35.04   $35.05   $35.00  
  7 purchase totals = $966.80       $1,032.7984   $1,032.78   $1,032.80   $1,032.70