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 $51.61   12.426%   $58.0231   $58.02   $58.00   $58.00  
  Purchase #2 $191.87   9.484%   $210.067   $210.07   $210.05   $210.10  
  Purchase #3 $103.60   6.846%   $110.6925   $110.69   $110.70   $110.70  
  Purchase #4 $94.68   12.544%   $106.5567   $106.56   $106.55   $106.60  
  Purchase #5 $156.97   13.178%   $177.6555   $177.66   $177.65   $177.70  
  Purchase #6 $239.44   8.533%   $259.8714   $259.87   $259.85   $259.90  
  Purchase #7 $160.51   8.224%   $173.7103   $173.71   $173.70   $173.70  
  7 purchase totals = $998.68       $1,096.5765   $1,096.58   $1,096.50   $1,096.70