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 $34.80   4.737%   $36.4485   $36.45   $36.45   $36.40  
  Purchase #2 $211.67   9.451%   $231.6749   $231.67   $231.65   $231.70  
  Purchase #3 $223.45   9.222%   $244.0566   $244.06   $244.05   $244.10  
  Purchase #4 $28.65   13.556%   $32.5338   $32.53   $32.55   $32.50  
  Purchase #5 $206.99   6.309%   $220.049   $220.05   $220.05   $220.00  
  Purchase #6 $70.45   9.588%   $77.2047   $77.20   $77.20   $77.20  
  Purchase #7 $200.38   11.478%   $223.3796   $223.38   $223.40   $223.40  
  7 purchase totals = $976.39       $1,065.3471   $1,065.34   $1,065.35   $1,065.30