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 $104.54   11.294%   $116.3467   $116.35   $116.35   $116.30  
  Purchase #2 $54.84   9.791%   $60.2094   $60.21   $60.20   $60.20  
  Purchase #3 $96.74   8.207%   $104.6795   $104.68   $104.70   $104.70  
  Purchase #4 $162.37   7.780%   $175.0024   $175.00   $175.00   $175.00  
  Purchase #5 $77.27   11.511%   $86.1645   $86.16   $86.15   $86.20  
  Purchase #6 $144.93   4.650%   $151.6692   $151.67   $151.65   $151.70  
  Purchase #7 $174.86   10.270%   $192.8181   $192.82   $192.80   $192.80  
  7 purchase totals = $815.55       $886.8898   $886.89   $886.85   $886.90