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 $122.69   7.425%   $131.7997   $131.80   $131.80   $131.80  
  Purchase #2 $136.83   11.544%   $152.6257   $152.63   $152.65   $152.60  
  Purchase #3 $96.75   4.738%   $101.334   $101.33   $101.35   $101.30  
  Purchase #4 $48.99   6.179%   $52.0171   $52.02   $52.00   $52.00  
  Purchase #5 $122.65   4.825%   $128.5679   $128.57   $128.55   $128.60  
  Purchase #6 $219.92   3.165%   $226.8805   $226.88   $226.90   $226.90  
  Purchase #7 $238.30   11.366%   $265.3852   $265.39   $265.40   $265.40  
  7 purchase totals = $986.13       $1,058.6101   $1,058.62   $1,058.65   $1,058.60