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 $211.43   10.219%   $233.036   $233.04   $233.05   $233.00  
  Purchase #2 $52.26   11.597%   $58.3206   $58.32   $58.30   $58.30  
  Purchase #3 $67.93   5.517%   $71.6777   $71.68   $71.70   $71.70  
  Purchase #4 $37.59   5.456%   $39.6409   $39.64   $39.65   $39.60  
  Purchase #5 $150.40   10.115%   $165.613   $165.61   $165.60   $165.60  
  Purchase #6 $56.70   7.864%   $61.1589   $61.16   $61.15   $61.20  
  Purchase #7 $140.92   6.250%   $149.7275   $149.73   $149.75   $149.70  
  7 purchase totals = $717.23       $779.1746   $779.18   $779.20   $779.10