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 $229.69   13.497%   $260.6913   $260.69   $260.70   $260.70  
  Purchase #2 $192.34   3.156%   $198.4103   $198.41   $198.40   $198.40  
  Purchase #3 $130.51   11.434%   $145.4325   $145.43   $145.45   $145.40  
  Purchase #4 $179.35   9.427%   $196.2573   $196.26   $196.25   $196.30  
  Purchase #5 $197.41   3.229%   $203.7844   $203.78   $203.80   $203.80  
  Purchase #6 $57.26   8.814%   $62.3069   $62.31   $62.30   $62.30  
  Purchase #7 $8.45   9.154%   $9.2235   $9.22   $9.20   $9.20  
  7 purchase totals = $995.01       $1,076.1062   $1,076.10   $1,076.10   $1,076.10