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 $88.34   6.774%   $94.3242   $94.32   $94.30   $94.30  
  Purchase #2 $240.42   12.166%   $269.6695   $269.67   $269.65   $269.70  
  Purchase #3 $114.80   7.451%   $123.3537   $123.35   $123.35   $123.40  
  Purchase #4 $88.32   9.287%   $96.5223   $96.52   $96.50   $96.50  
  Purchase #5 $130.31   4.545%   $136.2326   $136.23   $136.25   $136.20  
  Purchase #6 $99.37   8.230%   $107.5482   $107.55   $107.55   $107.50  
  Purchase #7 $160.43   8.291%   $173.7313   $173.73   $173.75   $173.70  
  7 purchase totals = $921.99       $1,001.3818   $1,001.37   $1,001.35   $1,001.30