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 $142.99   8.755%   $155.5088   $155.51   $155.50   $155.50  
  Purchase #2 $60.96   6.650%   $65.0138   $65.01   $65.00   $65.00  
  Purchase #3 $117.41   7.873%   $126.6537   $126.65   $126.65   $126.70  
  Purchase #4 $96.47   8.604%   $104.7703   $104.77   $104.75   $104.80  
  Purchase #5 $247.59   12.384%   $278.2515   $278.25   $278.25   $278.30  
  Purchase #6 $88.55   4.600%   $92.6233   $92.62   $92.60   $92.60  
  Purchase #7 $221.98   10.635%   $245.5876   $245.59   $245.60   $245.60  
  7 purchase totals = $975.95       $1,068.4090   $1,068.40   $1,068.35   $1,068.50