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 $105.47   13.662%   $119.8793   $119.88   $119.90   $119.90  
  Purchase #2 $243.97   5.220%   $256.7052   $256.71   $256.70   $256.70  
  Purchase #3 $6.97   12.119%   $7.8147   $7.81   $7.80   $7.80  
  Purchase #4 $167.26   6.214%   $177.6535   $177.65   $177.65   $177.70  
  Purchase #5 $232.35   13.414%   $263.5174   $263.52   $263.50   $263.50  
  Purchase #6 $156.86   6.701%   $167.3712   $167.37   $167.35   $167.40  
  Purchase #7 $182.44   8.152%   $197.3125   $197.31   $197.30   $197.30  
  7 purchase totals = $1,095.32       $1,190.2538   $1,190.25   $1,190.20   $1,190.30