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 $224.68   5.518%   $237.0778   $237.08   $237.10   $237.10  
  Purchase #2 $110.38   11.115%   $122.6487   $122.65   $122.65   $122.60  
  Purchase #3 $211.35   9.701%   $231.8531   $231.85   $231.85   $231.90  
  Purchase #4 $246.57   12.316%   $276.9376   $276.94   $276.95   $276.90  
  Purchase #5 $152.81   13.616%   $173.6166   $173.62   $173.60   $173.60  
  Purchase #6 $202.67   6.668%   $216.184   $216.18   $216.20   $216.20  
  Purchase #7 $79.67   11.169%   $88.5683   $88.57   $88.55   $88.60  
  7 purchase totals = $1,228.13       $1,346.8861   $1,346.89   $1,346.90   $1,346.90