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 $181.61   11.194%   $201.9394   $201.94   $201.95   $201.90  
  Purchase #2 $28.73   3.564%   $29.7539   $29.75   $29.75   $29.80  
  Purchase #3 $34.89   7.440%   $37.4858   $37.49   $37.50   $37.50  
  Purchase #4 $111.26   10.722%   $123.1893   $123.19   $123.20   $123.20  
  Purchase #5 $244.47   6.637%   $260.6955   $260.70   $260.70   $260.70  
  Purchase #6 $181.83   7.746%   $195.9146   $195.91   $195.90   $195.90  
  Purchase #7 $222.72   10.374%   $245.825   $245.83   $245.85   $245.80  
  7 purchase totals = $1,005.51       $1,094.8035   $1,094.81   $1,094.85   $1,094.80