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 $234.93   7.712%   $253.0478   $253.05   $253.05   $253.00  
  Purchase #2 $206.42   12.545%   $232.3154   $232.32   $232.30   $232.30  
  Purchase #3 $90.87   9.560%   $99.5572   $99.56   $99.55   $99.60  
  Purchase #4 $86.48   5.771%   $91.4708   $91.47   $91.45   $91.50  
  Purchase #5 $200.30   3.629%   $207.5689   $207.57   $207.55   $207.60  
  Purchase #6 $202.84   4.819%   $212.6149   $212.61   $212.60   $212.60  
  Purchase #7 $15.86   5.580%   $16.745   $16.75   $16.75   $16.70  
  7 purchase totals = $1,037.70       $1,113.3200   $1,113.33   $1,113.25   $1,113.30