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 $248.55   7.319%   $266.7414   $266.74   $266.75   $266.70  
  Purchase #2 $187.78   3.629%   $194.5945   $194.59   $194.60   $194.60  
  Purchase #3 $147.68   12.360%   $165.9332   $165.93   $165.95   $165.90  
  Purchase #4 $70.81   5.452%   $74.6706   $74.67   $74.65   $74.70  
  Purchase #5 $186.31   4.120%   $193.986   $193.99   $194.00   $194.00  
  Purchase #6 $132.58   9.460%   $145.1221   $145.12   $145.10   $145.10  
  Purchase #7 $10.78   10.428%   $11.9041   $11.90   $11.90   $11.90  
  7 purchase totals = $984.49       $1,052.9519   $1,052.94   $1,052.95   $1,052.90