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 $157.63   5.621%   $166.4904   $166.49   $166.50   $166.50  
  Purchase #2 $36.54   13.310%   $41.4035   $41.40   $41.40   $41.40  
  Purchase #3 $156.97   6.751%   $167.567   $167.57   $167.55   $167.60  
  Purchase #4 $118.57   7.578%   $127.5552   $127.56   $127.55   $127.60  
  Purchase #5 $177.35   13.705%   $201.6558   $201.66   $201.65   $201.70  
  Purchase #6 $230.45   12.379%   $258.9774   $258.98   $259.00   $259.00  
  Purchase #7 $168.46   8.687%   $183.0941   $183.09   $183.10   $183.10  
  7 purchase totals = $1,045.97       $1,146.7434   $1,146.75   $1,146.75   $1,146.90