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 $20.56   7.539%   $22.11   $22.11   $22.10   $22.10  
  Purchase #2 $21.84   11.210%   $24.2883   $24.29   $24.30   $24.30  
  Purchase #3 $228.47   4.194%   $238.052   $238.05   $238.05   $238.10  
  Purchase #4 $108.43   12.132%   $121.5847   $121.58   $121.60   $121.60  
  Purchase #5 $204.74   12.449%   $230.2281   $230.23   $230.25   $230.20  
  Purchase #6 $246.53   7.531%   $265.0962   $265.10   $265.10   $265.10  
  Purchase #7 $219.87   12.786%   $247.9826   $247.98   $248.00   $248.00  
  7 purchase totals = $1,050.44       $1,149.3419   $1,149.34   $1,149.40   $1,149.40