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 $228.53   7.569%   $245.8274   $245.83   $245.85   $245.80  
  Purchase #2 $50.89   4.119%   $52.9862   $52.99   $53.00   $53.00  
  Purchase #3 $179.49   13.614%   $203.9258   $203.93   $203.95   $203.90  
  Purchase #4 $34.37   6.262%   $36.5222   $36.52   $36.50   $36.50  
  Purchase #5 $23.54   12.270%   $26.4284   $26.43   $26.45   $26.40  
  Purchase #6 $46.57   8.648%   $50.5974   $50.60   $50.60   $50.60  
  Purchase #7 $54.52   4.873%   $57.1768   $57.18   $57.20   $57.20  
  7 purchase totals = $617.91       $673.4642   $673.48   $673.55   $673.40