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 $215.94   12.218%   $242.3235   $242.32   $242.30   $242.30  
  Purchase #2 $77.40   13.120%   $87.5549   $87.55   $87.55   $87.60  
  Purchase #3 $62.30   9.742%   $68.3693   $68.37   $68.35   $68.40  
  Purchase #4 $203.25   9.498%   $222.5547   $222.55   $222.55   $222.60  
  Purchase #5 $211.81   13.513%   $240.4319   $240.43   $240.45   $240.40  
  Purchase #6 $62.27   3.860%   $64.6736   $64.67   $64.65   $64.70  
  Purchase #7 $93.87   13.503%   $106.5453   $106.55   $106.55   $106.50  
  7 purchase totals = $926.84       $1,032.4532   $1,032.44   $1,032.40   $1,032.50