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 $243.93   8.229%   $264.003   $264.00   $264.00   $264.00  
  Purchase #2 $130.60   9.336%   $142.7928   $142.79   $142.80   $142.80  
  Purchase #3 $244.82   6.546%   $260.8459   $260.85   $260.85   $260.80  
  Purchase #4 $46.47   4.715%   $48.6611   $48.66   $48.65   $48.70  
  Purchase #5 $68.50   8.738%   $74.4855   $74.49   $74.50   $74.50  
  Purchase #6 $205.55   11.807%   $229.8193   $229.82   $229.80   $229.80  
  Purchase #7 $10.33   10.473%   $11.4119   $11.41   $11.40   $11.40  
  7 purchase totals = $950.20       $1,032.0195   $1,032.02   $1,032.00   $1,032.00