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 $154.70   6.841%   $165.283   $165.28   $165.30   $165.30  
  Purchase #2 $250.92   10.133%   $276.3457   $276.35   $276.35   $276.30  
  Purchase #3 $32.53   5.203%   $34.2225   $34.22   $34.20   $34.20  
  Purchase #4 $102.75   4.270%   $107.1374   $107.14   $107.15   $107.10  
  Purchase #5 $68.56   13.258%   $77.6497   $77.65   $77.65   $77.60  
  Purchase #6 $234.60   10.706%   $259.7163   $259.72   $259.70   $259.70  
  Purchase #7 $232.52   9.239%   $254.0025   $254.00   $254.00   $254.00  
  7 purchase totals = $1,076.58       $1,174.3571   $1,174.36   $1,174.35   $1,174.20