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 $44.48   9.507%   $48.7087   $48.71   $48.70   $48.70  
  Purchase #2 $219.25   7.445%   $235.5732   $235.57   $235.55   $235.60  
  Purchase #3 $108.73   13.710%   $123.6369   $123.64   $123.65   $123.60  
  Purchase #4 $239.69   13.729%   $272.597   $272.60   $272.60   $272.60  
  Purchase #5 $75.80   4.534%   $79.2368   $79.24   $79.25   $79.20  
  Purchase #6 $181.96   10.867%   $201.7336   $201.73   $201.75   $201.70  
  Purchase #7 $60.62   3.538%   $62.7647   $62.76   $62.75   $62.80  
  7 purchase totals = $930.53       $1,024.2509   $1,024.25   $1,024.25   $1,024.20