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 $64.36   10.866%   $71.3534   $71.35   $71.35   $71.40  
  Purchase #2 $220.75   13.863%   $251.3526   $251.35   $251.35   $251.40  
  Purchase #3 $10.78   11.213%   $11.9888   $11.99   $12.00   $12.00  
  Purchase #4 $62.67   13.663%   $71.2326   $71.23   $71.25   $71.20  
  Purchase #5 $192.32   3.134%   $198.3473   $198.35   $198.35   $198.30  
  Purchase #6 $187.70   7.718%   $202.1867   $202.19   $202.20   $202.20  
  Purchase #7 $207.73   11.789%   $232.2193   $232.22   $232.20   $232.20  
  7 purchase totals = $946.31       $1,038.6807   $1,038.68   $1,038.70   $1,038.70