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 $223.76   7.823%   $241.2647   $241.26   $241.25   $241.30  
  Purchase #2 $66.97   9.829%   $73.5525   $73.55   $73.55   $73.60  
  Purchase #3 $122.45   4.260%   $127.6664   $127.67   $127.65   $127.70  
  Purchase #4 $205.90   11.188%   $228.9361   $228.94   $228.95   $228.90  
  Purchase #5 $150.91   6.428%   $160.6105   $160.61   $160.60   $160.60  
  Purchase #6 $23.39   6.117%   $24.8208   $24.82   $24.80   $24.80  
  Purchase #7 $143.57   7.203%   $153.9113   $153.91   $153.90   $153.90  
  7 purchase totals = $936.95       $1,010.7623   $1,010.76   $1,010.70   $1,010.80