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 $209.75   3.193%   $216.4473   $216.45   $216.45   $216.40  
  Purchase #2 $169.48   7.272%   $181.8046   $181.80   $181.80   $181.80  
  Purchase #3 $130.52   6.216%   $138.6331   $138.63   $138.65   $138.60  
  Purchase #4 $168.47   9.524%   $184.5151   $184.52   $184.50   $184.50  
  Purchase #5 $97.31   9.651%   $106.7014   $106.70   $106.70   $106.70  
  Purchase #6 $47.52   6.652%   $50.681   $50.68   $50.70   $50.70  
  Purchase #7 $113.97   11.229%   $126.7677   $126.77   $126.75   $126.80  
  7 purchase totals = $937.02       $1,005.5502   $1,005.55   $1,005.55   $1,005.50