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 $229.27   9.553%   $251.1722   $251.17   $251.15   $251.20  
  Purchase #2 $245.44   12.792%   $276.8367   $276.84   $276.85   $276.80  
  Purchase #3 $124.92   8.475%   $135.507   $135.51   $135.50   $135.50  
  Purchase #4 $37.52   11.260%   $41.7448   $41.74   $41.75   $41.70  
  Purchase #5 $228.30   3.516%   $236.327   $236.33   $236.35   $236.30  
  Purchase #6 $119.60   6.608%   $127.5032   $127.50   $127.50   $127.50  
  Purchase #7 $181.46   9.414%   $198.5426   $198.54   $198.55   $198.50  
  7 purchase totals = $1,166.51       $1,267.6335   $1,267.63   $1,267.65   $1,267.50