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 $48.36   12.257%   $54.2875   $54.29   $54.30   $54.30  
  Purchase #2 $151.27   11.131%   $168.1079   $168.11   $168.10   $168.10  
  Purchase #3 $196.85   4.123%   $204.9661   $204.97   $204.95   $205.00  
  Purchase #4 $127.49   12.865%   $143.8916   $143.89   $143.90   $143.90  
  Purchase #5 $219.41   12.569%   $246.9876   $246.99   $247.00   $247.00  
  Purchase #6 $42.25   9.167%   $46.1231   $46.12   $46.10   $46.10  
  Purchase #7 $192.71   4.308%   $201.0119   $201.01   $201.00   $201.00  
  7 purchase totals = $978.34       $1,065.3757   $1,065.38   $1,065.35   $1,065.40