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 $88.87   5.258%   $93.5428   $93.54   $93.55   $93.50  
  Purchase #2 $171.58   11.117%   $190.6545   $190.65   $190.65   $190.70  
  Purchase #3 $134.81   6.536%   $143.6212   $143.62   $143.60   $143.60  
  Purchase #4 $139.98   3.515%   $144.9003   $144.90   $144.90   $144.90  
  Purchase #5 $34.29   7.850%   $36.9818   $36.98   $37.00   $37.00  
  Purchase #6 $225.90   8.837%   $245.8628   $245.86   $245.85   $245.90  
  Purchase #7 $214.99   6.257%   $228.4419   $228.44   $228.45   $228.40  
  7 purchase totals = $1,010.42       $1,084.0053   $1,083.99   $1,084.00   $1,084.00