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 $209.96   6.296%   $223.1791   $223.18   $223.20   $223.20  
  Purchase #2 $201.81   3.397%   $208.6655   $208.67   $208.65   $208.70  
  Purchase #3 $204.31   7.842%   $220.332   $220.33   $220.35   $220.30  
  Purchase #4 $237.79   8.352%   $257.6502   $257.65   $257.65   $257.70  
  Purchase #5 $60.92   13.284%   $69.0126   $69.01   $69.00   $69.00  
  Purchase #6 $116.97   13.710%   $133.0066   $133.01   $133.00   $133.00  
  Purchase #7 $88.55   5.589%   $93.4991   $93.50   $93.50   $93.50  
  7 purchase totals = $1,120.31       $1,205.3451   $1,205.35   $1,205.35   $1,205.40