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 $44.61   10.256%   $49.1852   $49.19   $49.20   $49.20  
  Purchase #2 $232.53   3.478%   $240.6174   $240.62   $240.60   $240.60  
  Purchase #3 $30.62   7.529%   $32.9254   $32.93   $32.95   $32.90  
  Purchase #4 $211.70   5.795%   $223.968   $223.97   $223.95   $224.00  
  Purchase #5 $85.83   10.170%   $94.5589   $94.56   $94.55   $94.60  
  Purchase #6 $230.65   12.201%   $258.7916   $258.79   $258.80   $258.80  
  Purchase #7 $240.59   7.773%   $259.2911   $259.29   $259.30   $259.30  
  7 purchase totals = $1,076.53       $1,159.3376   $1,159.35   $1,159.35   $1,159.40