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 $243.85   12.501%   $274.3337   $274.33   $274.35   $274.30  
  Purchase #2 $129.53   4.715%   $135.6373   $135.64   $135.65   $135.60  
  Purchase #3 $34.99   7.843%   $37.7343   $37.73   $37.75   $37.70  
  Purchase #4 $16.54   5.176%   $17.3961   $17.40   $17.40   $17.40  
  Purchase #5 $218.55   9.693%   $239.7341   $239.73   $239.75   $239.70  
  Purchase #6 $59.55   6.825%   $63.6143   $63.61   $63.60   $63.60  
  Purchase #7 $84.94   9.241%   $92.7893   $92.79   $92.80   $92.80  
  7 purchase totals = $787.95       $861.2391   $861.23   $861.30   $861.10