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 $12.41   11.806%   $13.8751   $13.88   $13.90   $13.90  
  Purchase #2 $70.84   6.790%   $75.65   $75.65   $75.65   $75.70  
  Purchase #3 $95.87   7.225%   $102.7966   $102.80   $102.80   $102.80  
  Purchase #4 $215.98   9.714%   $236.9603   $236.96   $236.95   $237.00  
  Purchase #5 $161.50   7.127%   $173.0101   $173.01   $173.00   $173.00  
  Purchase #6 $220.41   12.755%   $248.5233   $248.52   $248.50   $248.50  
  Purchase #7 $192.80   7.683%   $207.6128   $207.61   $207.60   $207.60  
  7 purchase totals = $969.81       $1,058.4282   $1,058.43   $1,058.40   $1,058.50