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 $84.57   7.252%   $90.703   $90.70   $90.70   $90.70  
  Purchase #2 $168.53   8.519%   $182.8871   $182.89   $182.90   $182.90  
  Purchase #3 $186.83   9.493%   $204.5658   $204.57   $204.55   $204.60  
  Purchase #4 $97.53   13.781%   $110.9706   $110.97   $110.95   $111.00  
  Purchase #5 $169.56   5.648%   $179.1367   $179.14   $179.15   $179.10  
  Purchase #6 $213.28   8.585%   $231.5901   $231.59   $231.60   $231.60  
  Purchase #7 $56.71   12.257%   $63.6609   $63.66   $63.65   $63.70  
  7 purchase totals = $977.01       $1,063.5142   $1,063.52   $1,063.50   $1,063.60