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 $195.57   12.134%   $219.3005   $219.30   $219.30   $219.30  
  Purchase #2 $177.86   3.396%   $183.9001   $183.90   $183.90   $183.90  
  Purchase #3 $113.52   9.347%   $124.1307   $124.13   $124.15   $124.10  
  Purchase #4 $138.63   11.820%   $155.0161   $155.02   $155.00   $155.00  
  Purchase #5 $213.67   6.621%   $227.8171   $227.82   $227.80   $227.80  
  Purchase #6 $187.52   9.673%   $205.6588   $205.66   $205.65   $205.70  
  Purchase #7 $158.29   11.433%   $176.3873   $176.39   $176.40   $176.40  
  7 purchase totals = $1,185.06       $1,292.2106   $1,292.22   $1,292.20   $1,292.20