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 $246.54   8.630%   $267.8164   $267.82   $267.80   $267.80  
  Purchase #2 $215.88   12.585%   $243.0485   $243.05   $243.05   $243.00  
  Purchase #3 $84.67   13.224%   $95.8668   $95.87   $95.85   $95.90  
  Purchase #4 $25.74   12.379%   $28.9264   $28.93   $28.95   $28.90  
  Purchase #5 $14.55   13.734%   $16.5483   $16.55   $16.55   $16.50  
  Purchase #6 $139.25   4.650%   $145.7251   $145.73   $145.75   $145.70  
  Purchase #7 $199.48   13.647%   $226.703   $226.70   $226.70   $226.70  
  7 purchase totals = $926.11       $1,024.6345   $1,024.65   $1,024.65   $1,024.50