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 $58.50   13.380%   $66.3273   $66.33   $66.35   $66.30  
  Purchase #2 $121.84   9.799%   $133.7791   $133.78   $133.80   $133.80  
  Purchase #3 $135.35   13.436%   $153.5356   $153.54   $153.55   $153.50  
  Purchase #4 $234.25   3.348%   $242.0927   $242.09   $242.10   $242.10  
  Purchase #5 $147.56   3.630%   $152.9164   $152.92   $152.90   $152.90  
  Purchase #6 $189.94   4.788%   $199.0343   $199.03   $199.05   $199.00  
  Purchase #7 $137.84   5.509%   $145.4336   $145.43   $145.45   $145.40  
  7 purchase totals = $1,025.28       $1,093.1190   $1,093.12   $1,093.20   $1,093.00