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 $88.61   12.504%   $99.6898   $99.69   $99.70   $99.70  
  Purchase #2 $183.52   10.434%   $202.6685   $202.67   $202.65   $202.70  
  Purchase #3 $122.46   3.346%   $126.5575   $126.56   $126.55   $126.60  
  Purchase #4 $98.27   6.268%   $104.4296   $104.43   $104.45   $104.40  
  Purchase #5 $173.69   6.692%   $185.3133   $185.31   $185.30   $185.30  
  Purchase #6 $193.27   5.569%   $204.0332   $204.03   $204.05   $204.00  
  Purchase #7 $129.94   12.819%   $146.597   $146.60   $146.60   $146.60  
  7 purchase totals = $989.76       $1,069.2889   $1,069.29   $1,069.30   $1,069.30