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 $55.66   7.344%   $59.7477   $59.75   $59.75   $59.70  
  Purchase #2 $223.45   13.189%   $252.9208   $252.92   $252.90   $252.90  
  Purchase #3 $249.72   11.251%   $277.816   $277.82   $277.80   $277.80  
  Purchase #4 $37.91   10.660%   $41.9512   $41.95   $41.95   $42.00  
  Purchase #5 $112.79   12.295%   $126.6575   $126.66   $126.65   $126.70  
  Purchase #6 $81.78   3.409%   $84.5679   $84.57   $84.55   $84.60  
  Purchase #7 $235.97   13.592%   $268.043   $268.04   $268.05   $268.00  
  7 purchase totals = $997.28       $1,111.7041   $1,111.71   $1,111.65   $1,111.70