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 $183.58   10.600%   $203.0395   $203.04   $203.05   $203.00  
  Purchase #2 $62.31   3.347%   $64.3955   $64.40   $64.40   $64.40  
  Purchase #3 $169.39   9.585%   $185.626   $185.63   $185.65   $185.60  
  Purchase #4 $233.45   9.372%   $255.3289   $255.33   $255.35   $255.30  
  Purchase #5 $20.68   9.508%   $22.6463   $22.65   $22.65   $22.60  
  Purchase #6 $201.42   5.116%   $211.7246   $211.72   $211.70   $211.70  
  Purchase #7 $112.83   4.864%   $118.3181   $118.32   $118.30   $118.30  
  7 purchase totals = $983.66       $1,061.0789   $1,061.09   $1,061.10   $1,060.90