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 $218.83   10.118%   $240.9712   $240.97   $240.95   $241.00  
  Purchase #2 $190.99   10.690%   $211.4068   $211.41   $211.40   $211.40  
  Purchase #3 $175.79   12.234%   $197.2961   $197.30   $197.30   $197.30  
  Purchase #4 $167.59   4.167%   $174.5735   $174.57   $174.55   $174.60  
  Purchase #5 $49.90   12.489%   $56.132   $56.13   $56.15   $56.10  
  Purchase #6 $36.47   11.377%   $40.6192   $40.62   $40.60   $40.60  
  Purchase #7 $120.51   12.523%   $135.6015   $135.60   $135.60   $135.60  
  7 purchase totals = $960.08       $1,056.6003   $1,056.60   $1,056.55   $1,056.60