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 $227.61   11.816%   $254.5044   $254.50   $254.50   $254.50  
  Purchase #2 $26.79   8.357%   $29.0288   $29.03   $29.05   $29.00  
  Purchase #3 $63.93   6.436%   $68.0445   $68.04   $68.05   $68.00  
  Purchase #4 $118.59   9.834%   $130.2521   $130.25   $130.25   $130.30  
  Purchase #5 $92.41   8.521%   $100.2843   $100.28   $100.30   $100.30  
  Purchase #6 $238.91   10.577%   $264.1795   $264.18   $264.20   $264.20  
  Purchase #7 $159.73   8.143%   $172.7368   $172.74   $172.75   $172.70  
  7 purchase totals = $927.97       $1,019.0304   $1,019.02   $1,019.10   $1,019.00