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 $169.49   12.426%   $190.5508   $190.55   $190.55   $190.60  
  Purchase #2 $227.61   3.538%   $235.6628   $235.66   $235.65   $235.70  
  Purchase #3 $210.60   9.413%   $230.4238   $230.42   $230.40   $230.40  
  Purchase #4 $65.89   3.337%   $68.0887   $68.09   $68.10   $68.10  
  Purchase #5 $87.26   12.352%   $98.0384   $98.04   $98.05   $98.00  
  Purchase #6 $136.57   9.117%   $149.0211   $149.02   $149.00   $149.00  
  Purchase #7 $86.97   7.544%   $93.531   $93.53   $93.55   $93.50  
  7 purchase totals = $984.39       $1,065.3166   $1,065.31   $1,065.30   $1,065.30