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 $62.71   4.552%   $65.5646   $65.56   $65.55   $65.60  
  Purchase #2 $68.53   4.623%   $71.6981   $71.70   $71.70   $71.70  
  Purchase #3 $234.68   6.794%   $250.6242   $250.62   $250.60   $250.60  
  Purchase #4 $112.62   10.300%   $124.2199   $124.22   $124.20   $124.20  
  Purchase #5 $219.88   3.317%   $227.1734   $227.17   $227.15   $227.20  
  Purchase #6 $159.78   12.444%   $179.663   $179.66   $179.65   $179.70  
  Purchase #7 $141.45   13.373%   $160.3661   $160.37   $160.35   $160.40  
  7 purchase totals = $999.65       $1,079.3093   $1,079.30   $1,079.20   $1,079.40