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 $204.35   5.493%   $215.5749   $215.57   $215.55   $215.60  
  Purchase #2 $184.65   6.132%   $195.9727   $195.97   $195.95   $196.00  
  Purchase #3 $229.68   4.713%   $240.5048   $240.50   $240.50   $240.50  
  Purchase #4 $187.36   7.825%   $202.0209   $202.02   $202.00   $202.00  
  Purchase #5 $8.86   5.829%   $9.3764   $9.38   $9.40   $9.40  
  Purchase #6 $54.31   5.581%   $57.341   $57.34   $57.35   $57.30  
  Purchase #7 $78.32   11.738%   $87.5132   $87.51   $87.50   $87.50  
  7 purchase totals = $947.53       $1,008.3039   $1,008.29   $1,008.25   $1,008.30