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 $32.28   5.251%   $33.975   $33.98   $34.00   $34.00  
  Purchase #2 $130.89   12.347%   $147.051   $147.05   $147.05   $147.10  
  Purchase #3 $94.58   9.118%   $103.2038   $103.20   $103.20   $103.20  
  Purchase #4 $167.90   4.799%   $175.9575   $175.96   $175.95   $176.00  
  Purchase #5 $30.30   6.158%   $32.1659   $32.17   $32.15   $32.20  
  Purchase #6 $15.82   6.791%   $16.8943   $16.89   $16.90   $16.90  
  Purchase #7 $33.87   11.716%   $37.8382   $37.84   $37.85   $37.80  
  7 purchase totals = $505.64       $547.0857   $547.09   $547.10   $547.20