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 $152.51   6.858%   $162.9691   $162.97   $162.95   $163.00  
  Purchase #2 $212.29   6.823%   $226.7745   $226.77   $226.75   $226.80  
  Purchase #3 $60.96   12.463%   $68.5574   $68.56   $68.55   $68.60  
  Purchase #4 $142.73   10.412%   $157.591   $157.59   $157.60   $157.60  
  Purchase #5 $72.33   9.301%   $79.0574   $79.06   $79.05   $79.10  
  Purchase #6 $202.53   8.763%   $220.2777   $220.28   $220.30   $220.30  
  Purchase #7 $118.25   10.700%   $130.9028   $130.90   $130.90   $130.90  
  7 purchase totals = $961.60       $1,046.1299   $1,046.13   $1,046.10   $1,046.30