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 $220.58   10.621%   $244.0078   $244.01   $244.00   $244.00  
  Purchase #2 $163.52   12.545%   $184.0336   $184.03   $184.05   $184.00  
  Purchase #3 $230.38   13.294%   $261.0067   $261.01   $261.00   $261.00  
  Purchase #4 $72.54   13.608%   $82.4112   $82.41   $82.40   $82.40  
  Purchase #5 $160.56   9.375%   $175.6125   $175.61   $175.60   $175.60  
  Purchase #6 $54.28   12.441%   $61.033   $61.03   $61.05   $61.00  
  Purchase #7 $205.57   13.325%   $232.9622   $232.96   $232.95   $233.00  
  7 purchase totals = $1,107.43       $1,241.0670   $1,241.06   $1,241.05   $1,241.00