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 $201.42   7.617%   $216.7622   $216.76   $216.75   $216.80  
  Purchase #2 $88.41   11.702%   $98.7557   $98.76   $98.75   $98.80  
  Purchase #3 $160.26   12.801%   $180.7749   $180.77   $180.75   $180.80  
  Purchase #4 $49.74   8.468%   $53.952   $53.95   $53.95   $54.00  
  Purchase #5 $220.45   6.433%   $234.6315   $234.63   $234.65   $234.60  
  Purchase #6 $189.52   13.355%   $214.8304   $214.83   $214.85   $214.80  
  Purchase #7 $102.28   13.504%   $116.0919   $116.09   $116.10   $116.10  
  7 purchase totals = $1,012.08       $1,115.7986   $1,115.79   $1,115.80   $1,115.90