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 $234.64   11.146%   $260.793   $260.79   $260.80   $260.80  
  Purchase #2 $32.79   8.220%   $35.4853   $35.49   $35.50   $35.50  
  Purchase #3 $233.42   11.396%   $260.0205   $260.02   $260.00   $260.00  
  Purchase #4 $26.42   12.701%   $29.7756   $29.78   $29.80   $29.80  
  Purchase #5 $197.48   12.220%   $221.6121   $221.61   $221.60   $221.60  
  Purchase #6 $126.30   3.215%   $130.3605   $130.36   $130.35   $130.40  
  Purchase #7 $179.30   4.732%   $187.7845   $187.78   $187.80   $187.80  
  7 purchase totals = $1,030.35       $1,125.8315   $1,125.83   $1,125.85   $1,125.90