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 $162.31   6.704%   $173.1913   $173.19   $173.20   $173.20  
  Purchase #2 $242.52   3.771%   $251.6654   $251.67   $251.65   $251.70  
  Purchase #3 $16.49   7.188%   $17.6753   $17.68   $17.70   $17.70  
  Purchase #4 $23.28   7.188%   $24.9534   $24.95   $24.95   $25.00  
  Purchase #5 $148.67   11.465%   $165.715   $165.72   $165.70   $165.70  
  Purchase #6 $235.39   3.501%   $243.631   $243.63   $243.65   $243.60  
  Purchase #7 $134.78   3.283%   $139.2048   $139.20   $139.20   $139.20  
  7 purchase totals = $963.44       $1,016.0362   $1,016.04   $1,016.05   $1,016.10