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 $24.43   8.783%   $26.5757   $26.58   $26.60   $26.60  
  Purchase #2 $232.81   10.679%   $257.6718   $257.67   $257.65   $257.70  
  Purchase #3 $167.98   11.723%   $187.6723   $187.67   $187.65   $187.70  
  Purchase #4 $216.65   5.592%   $228.7651   $228.77   $228.75   $228.80  
  Purchase #5 $215.86   9.812%   $237.0402   $237.04   $237.05   $237.00  
  Purchase #6 $42.87   12.808%   $48.3608   $48.36   $48.35   $48.40  
  Purchase #7 $59.54   8.672%   $64.7033   $64.70   $64.70   $64.70  
  7 purchase totals = $960.14       $1,050.7892   $1,050.79   $1,050.75   $1,050.90