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 $178.35   13.674%   $202.7376   $202.74   $202.75   $202.70  
  Purchase #2 $226.74   4.756%   $237.5238   $237.52   $237.50   $237.50  
  Purchase #3 $68.32   11.460%   $76.1495   $76.15   $76.15   $76.10  
  Purchase #4 $174.34   10.841%   $193.2402   $193.24   $193.25   $193.20  
  Purchase #5 $97.39   8.851%   $106.01   $106.01   $106.00   $106.00  
  Purchase #6 $31.37   6.839%   $33.5154   $33.52   $33.50   $33.50  
  Purchase #7 $149.33   9.182%   $163.0415   $163.04   $163.05   $163.00  
  7 purchase totals = $925.84       $1,012.2180   $1,012.22   $1,012.20   $1,012.00