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 $99.57   7.870%   $107.4062   $107.41   $107.40   $107.40  
  Purchase #2 $28.25   12.710%   $31.8406   $31.84   $31.85   $31.80  
  Purchase #3 $124.43   3.669%   $128.9953   $129.00   $129.00   $129.00  
  Purchase #4 $223.75   7.593%   $240.7393   $240.74   $240.75   $240.70  
  Purchase #5 $144.53   10.264%   $159.3646   $159.36   $159.35   $159.40  
  Purchase #6 $244.86   13.173%   $277.1154   $277.12   $277.10   $277.10  
  Purchase #7 $144.88   5.680%   $153.1092   $153.11   $153.10   $153.10  
  7 purchase totals = $1,010.27       $1,098.5706   $1,098.58   $1,098.55   $1,098.50