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 $93.70   3.258%   $96.7527   $96.75   $96.75   $96.80  
  Purchase #2 $144.46   9.270%   $157.8514   $157.85   $157.85   $157.90  
  Purchase #3 $98.34   11.364%   $109.5154   $109.52   $109.50   $109.50  
  Purchase #4 $191.46   12.353%   $215.1111   $215.11   $215.10   $215.10  
  Purchase #5 $118.38   5.146%   $124.4718   $124.47   $124.45   $124.50  
  Purchase #6 $41.96   13.160%   $47.4819   $47.48   $47.50   $47.50  
  Purchase #7 $198.65   10.723%   $219.9512   $219.95   $219.95   $220.00  
  7 purchase totals = $886.95       $971.1355   $971.13   $971.10   $971.30