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 $206.31   9.539%   $225.9899   $225.99   $226.00   $226.00  
  Purchase #2 $154.98   8.276%   $167.8061   $167.81   $167.80   $167.80  
  Purchase #3 $198.77   6.437%   $211.5648   $211.56   $211.55   $211.60  
  Purchase #4 $58.59   13.845%   $66.7018   $66.70   $66.70   $66.70  
  Purchase #5 $24.77   4.718%   $25.9386   $25.94   $25.95   $25.90  
  Purchase #6 $229.55   13.537%   $260.6242   $260.62   $260.60   $260.60  
  Purchase #7 $125.41   3.179%   $129.3968   $129.40   $129.40   $129.40  
  7 purchase totals = $998.38       $1,088.0222   $1,088.02   $1,088.00   $1,088.00