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 $194.42   6.273%   $206.616   $206.62   $206.60   $206.60  
  Purchase #2 $28.42   11.451%   $31.6744   $31.67   $31.65   $31.70  
  Purchase #3 $224.34   10.558%   $248.0258   $248.03   $248.05   $248.00  
  Purchase #4 $88.90   8.203%   $96.1925   $96.19   $96.20   $96.20  
  Purchase #5 $34.86   6.295%   $37.0544   $37.05   $37.05   $37.10  
  Purchase #6 $248.95   11.580%   $277.7784   $277.78   $277.80   $277.80  
  Purchase #7 $135.83   7.504%   $146.0227   $146.02   $146.00   $146.00  
  7 purchase totals = $955.72       $1,043.3642   $1,043.36   $1,043.35   $1,043.40