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 $201.46   8.513%   $218.6103   $218.61   $218.60   $218.60  
  Purchase #2 $213.29   3.444%   $220.6357   $220.64   $220.65   $220.60  
  Purchase #3 $55.95   11.144%   $62.1851   $62.19   $62.20   $62.20  
  Purchase #4 $239.80   12.422%   $269.588   $269.59   $269.60   $269.60  
  Purchase #5 $175.49   6.649%   $187.1583   $187.16   $187.15   $187.20  
  Purchase #6 $186.45   12.466%   $209.6929   $209.69   $209.70   $209.70  
  Purchase #7 $79.89   4.279%   $83.3085   $83.31   $83.30   $83.30  
  7 purchase totals = $1,152.33       $1,251.1788   $1,251.19   $1,251.20   $1,251.20