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 $165.48   10.745%   $183.2608   $183.26   $183.25   $183.30  
  Purchase #2 $177.33   12.597%   $199.6683   $199.67   $199.65   $199.70  
  Purchase #3 $190.62   10.644%   $210.9096   $210.91   $210.90   $210.90  
  Purchase #4 $31.92   10.126%   $35.1522   $35.15   $35.15   $35.20  
  Purchase #5 $59.57   5.383%   $62.7767   $62.78   $62.80   $62.80  
  Purchase #6 $181.89   3.449%   $188.1634   $188.16   $188.15   $188.20  
  Purchase #7 $189.60   7.467%   $203.7574   $203.76   $203.75   $203.80  
  7 purchase totals = $996.41       $1,083.6884   $1,083.69   $1,083.65   $1,083.90