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 $37.86   9.153%   $41.3253   $41.33   $41.35   $41.30  
  Purchase #2 $181.48   11.826%   $202.9418   $202.94   $202.95   $202.90  
  Purchase #3 $166.69   3.187%   $172.0024   $172.00   $172.00   $172.00  
  Purchase #4 $216.61   11.351%   $241.1974   $241.20   $241.20   $241.20  
  Purchase #5 $49.51   11.715%   $55.3101   $55.31   $55.30   $55.30  
  Purchase #6 $240.62   13.255%   $272.5142   $272.51   $272.50   $272.50  
  Purchase #7 $34.43   13.829%   $39.1913   $39.19   $39.20   $39.20  
  7 purchase totals = $927.20       $1,024.4825   $1,024.48   $1,024.50   $1,024.40