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 $31.35   7.445%   $33.684   $33.68   $33.70   $33.70  
  Purchase #2 $198.99   12.244%   $223.3543   $223.35   $223.35   $223.40  
  Purchase #3 $117.66   12.837%   $132.764   $132.76   $132.75   $132.80  
  Purchase #4 $17.65   9.102%   $19.2565   $19.26   $19.25   $19.30  
  Purchase #5 $165.25   11.845%   $184.8239   $184.82   $184.80   $184.80  
  Purchase #6 $162.65   11.798%   $181.8394   $181.84   $181.85   $181.80  
  Purchase #7 $23.97   5.531%   $25.2958   $25.30   $25.30   $25.30  
  7 purchase totals = $717.52       $801.0179   $801.01   $801.00   $801.10