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 $36.58   12.203%   $41.0439   $41.04   $41.05   $41.00  
  Purchase #2 $230.57   4.320%   $240.5306   $240.53   $240.55   $240.50  
  Purchase #3 $95.49   8.211%   $103.3307   $103.33   $103.35   $103.30  
  Purchase #4 $194.59   13.248%   $220.3693   $220.37   $220.35   $220.40  
  Purchase #5 $235.34   8.335%   $254.9556   $254.96   $254.95   $255.00  
  Purchase #6 $158.75   4.578%   $166.0176   $166.02   $166.00   $166.00  
  Purchase #7 $219.42   3.330%   $226.7267   $226.73   $226.75   $226.70  
  7 purchase totals = $1,170.74       $1,252.9744   $1,252.98   $1,253.00   $1,252.90