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 $36.79   13.170%   $41.6352   $41.64   $41.65   $41.60  
  Purchase #2 $232.52   3.560%   $240.7977   $240.80   $240.80   $240.80  
  Purchase #3 $60.32   7.386%   $64.7752   $64.78   $64.80   $64.80  
  Purchase #4 $125.92   13.823%   $143.3259   $143.33   $143.35   $143.30  
  Purchase #5 $214.92   7.348%   $230.7123   $230.71   $230.70   $230.70  
  Purchase #6 $182.75   9.666%   $200.4146   $200.41   $200.40   $200.40  
  Purchase #7 $125.66   3.665%   $130.2654   $130.27   $130.25   $130.30  
  7 purchase totals = $978.88       $1,051.9263   $1,051.94   $1,051.95   $1,051.90