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 $15.84   4.297%   $16.5206   $16.52   $16.50   $16.50  
  Purchase #2 $216.94   12.391%   $243.821   $243.82   $243.80   $243.80  
  Purchase #3 $178.62   5.209%   $187.9243   $187.92   $187.90   $187.90  
  Purchase #4 $19.96   12.742%   $22.5033   $22.50   $22.50   $22.50  
  Purchase #5 $212.80   7.281%   $228.294   $228.29   $228.30   $228.30  
  Purchase #6 $250.82   6.118%   $266.1652   $266.17   $266.15   $266.20  
  Purchase #7 $60.91   11.789%   $68.0907   $68.09   $68.10   $68.10  
  7 purchase totals = $955.89       $1,033.3191   $1,033.31   $1,033.25   $1,033.30