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 $184.58   6.743%   $197.0262   $197.03   $197.05   $197.00  
  Purchase #2 $138.35   13.430%   $156.9304   $156.93   $156.95   $156.90  
  Purchase #3 $208.50   6.548%   $222.1526   $222.15   $222.15   $222.20  
  Purchase #4 $162.46   10.827%   $180.0495   $180.05   $180.05   $180.00  
  Purchase #5 $59.86   12.799%   $67.5215   $67.52   $67.50   $67.50  
  Purchase #6 $167.37   6.270%   $177.8641   $177.86   $177.85   $177.90  
  Purchase #7 $124.54   7.279%   $133.6053   $133.61   $133.60   $133.60  
  7 purchase totals = $1,045.66       $1,135.1496   $1,135.15   $1,135.15   $1,135.10