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 $84.61   9.801%   $92.9026   $92.90   $92.90   $92.90  
  Purchase #2 $141.93   3.604%   $147.0452   $147.05   $147.05   $147.00  
  Purchase #3 $71.98   5.580%   $75.9965   $76.00   $76.00   $76.00  
  Purchase #4 $41.32   6.555%   $44.0285   $44.03   $44.05   $44.00  
  Purchase #5 $194.93   12.246%   $218.8011   $218.80   $218.80   $218.80  
  Purchase #6 $191.80   7.629%   $206.4324   $206.43   $206.45   $206.40  
  Purchase #7 $180.98   5.844%   $191.5565   $191.56   $191.55   $191.60  
  7 purchase totals = $907.55       $976.7628   $976.77   $976.80   $976.70