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 $233.59   13.533%   $265.2017   $265.20   $265.20   $265.20  
  Purchase #2 $126.91   10.828%   $140.6518   $140.65   $140.65   $140.70  
  Purchase #3 $62.96   4.128%   $65.559   $65.56   $65.55   $65.60  
  Purchase #4 $65.43   5.245%   $68.8618   $68.86   $68.85   $68.90  
  Purchase #5 $205.87   10.207%   $226.8832   $226.88   $226.90   $226.90  
  Purchase #6 $88.41   5.226%   $93.0303   $93.03   $93.05   $93.00  
  Purchase #7 $206.36   9.433%   $225.8259   $225.83   $225.85   $225.80  
  7 purchase totals = $989.53       $1,086.0137   $1,086.01   $1,086.05   $1,086.10