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 $58.83   10.527%   $65.023   $65.02   $65.00   $65.00  
  Purchase #2 $24.25   6.768%   $25.8912   $25.89   $25.90   $25.90  
  Purchase #3 $249.77   7.673%   $268.9349   $268.93   $268.95   $268.90  
  Purchase #4 $232.84   9.476%   $254.9039   $254.90   $254.90   $254.90  
  Purchase #5 $126.37   6.211%   $134.2188   $134.22   $134.20   $134.20  
  Purchase #6 $211.72   8.726%   $230.1947   $230.19   $230.20   $230.20  
  Purchase #7 $53.79   4.506%   $56.2138   $56.21   $56.20   $56.20  
  7 purchase totals = $957.57       $1,035.3803   $1,035.36   $1,035.35   $1,035.30