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 $213.67   13.121%   $241.7056   $241.71   $241.70   $241.70  
  Purchase #2 $237.28   12.611%   $267.2034   $267.20   $267.20   $267.20  
  Purchase #3 $150.73   6.343%   $160.2908   $160.29   $160.30   $160.30  
  Purchase #4 $232.70   3.523%   $240.898   $240.90   $240.90   $240.90  
  Purchase #5 $247.98   11.627%   $276.8126   $276.81   $276.80   $276.80  
  Purchase #6 $144.84   3.851%   $150.4178   $150.42   $150.40   $150.40  
  Purchase #7 $80.84   13.672%   $91.8924   $91.89   $91.90   $91.90  
  7 purchase totals = $1,308.04       $1,429.2206   $1,429.22   $1,429.20   $1,429.20