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 $41.94   5.236%   $44.136   $44.14   $44.15   $44.10  
  Purchase #2 $156.76   12.287%   $176.0211   $176.02   $176.00   $176.00  
  Purchase #3 $220.55   11.331%   $245.5405   $245.54   $245.55   $245.50  
  Purchase #4 $76.87   9.862%   $84.4509   $84.45   $84.45   $84.50  
  Purchase #5 $235.74   4.692%   $246.8009   $246.80   $246.80   $246.80  
  Purchase #6 $59.64   4.156%   $62.1186   $62.12   $62.10   $62.10  
  Purchase #7 $246.76   5.204%   $259.6014   $259.60   $259.60   $259.60  
  7 purchase totals = $1,038.26       $1,118.6694   $1,118.67   $1,118.65   $1,118.60