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 $172.95   12.362%   $194.3301   $194.33   $194.35   $194.30  
  Purchase #2 $8.72   7.737%   $9.3947   $9.39   $9.40   $9.40  
  Purchase #3 $114.96   10.725%   $127.2895   $127.29   $127.30   $127.30  
  Purchase #4 $84.27   10.254%   $92.911   $92.91   $92.90   $92.90  
  Purchase #5 $138.90   4.806%   $145.5755   $145.58   $145.60   $145.60  
  Purchase #6 $168.52   7.169%   $180.6012   $180.60   $180.60   $180.60  
  Purchase #7 $240.32   13.220%   $272.0903   $272.09   $272.10   $272.10  
  7 purchase totals = $928.64       $1,022.1923   $1,022.19   $1,022.25   $1,022.20