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 $59.59   9.402%   $65.1927   $65.19   $65.20   $65.20  
  Purchase #2 $177.39   11.450%   $197.7012   $197.70   $197.70   $197.70  
  Purchase #3 $108.50   4.382%   $113.2545   $113.25   $113.25   $113.30  
  Purchase #4 $199.68   10.332%   $220.3109   $220.31   $220.30   $220.30  
  Purchase #5 $141.49   8.701%   $153.801   $153.80   $153.80   $153.80  
  Purchase #6 $13.73   4.789%   $14.3875   $14.39   $14.40   $14.40  
  Purchase #7 $221.49   6.579%   $236.0618   $236.06   $236.05   $236.10  
  7 purchase totals = $921.87       $1,000.7096   $1,000.70   $1,000.70   $1,000.80