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 $219.52   10.353%   $242.2469   $242.25   $242.25   $242.20  
  Purchase #2 $182.90   10.248%   $201.6436   $201.64   $201.65   $201.60  
  Purchase #3 $94.96   7.379%   $101.9671   $101.97   $101.95   $102.00  
  Purchase #4 $59.48   4.819%   $62.3463   $62.35   $62.35   $62.30  
  Purchase #5 $133.37   10.746%   $147.7019   $147.70   $147.70   $147.70  
  Purchase #6 $169.53   4.367%   $176.9334   $176.93   $176.95   $176.90  
  Purchase #7 $117.47   5.379%   $123.7887   $123.79   $123.80   $123.80  
  7 purchase totals = $977.23       $1,056.6279   $1,056.63   $1,056.65   $1,056.50