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 $218.49   13.657%   $248.3292   $248.33   $248.35   $248.30  
  Purchase #2 $179.92   9.781%   $197.518   $197.52   $197.50   $197.50  
  Purchase #3 $223.40   12.604%   $251.5573   $251.56   $251.55   $251.60  
  Purchase #4 $88.97   3.383%   $91.9799   $91.98   $92.00   $92.00  
  Purchase #5 $66.80   6.836%   $71.3664   $71.37   $71.35   $71.40  
  Purchase #6 $171.37   13.793%   $195.0071   $195.01   $195.00   $195.00  
  Purchase #7 $195.95   6.437%   $208.5633   $208.56   $208.55   $208.60  
  7 purchase totals = $1,144.90       $1,264.3212   $1,264.33   $1,264.30   $1,264.40