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 $194.66   12.761%   $219.5006   $219.50   $219.50   $219.50  
  Purchase #2 $241.33   3.519%   $249.8224   $249.82   $249.80   $249.80  
  Purchase #3 $47.46   8.141%   $51.3237   $51.32   $51.30   $51.30  
  Purchase #4 $26.39   10.540%   $29.1715   $29.17   $29.15   $29.20  
  Purchase #5 $245.52   11.577%   $273.9439   $273.94   $273.95   $273.90  
  Purchase #6 $184.81   4.313%   $192.7809   $192.78   $192.80   $192.80  
  Purchase #7 $14.26   9.815%   $15.6596   $15.66   $15.65   $15.70  
  7 purchase totals = $954.43       $1,032.2026   $1,032.19   $1,032.15   $1,032.20