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 $203.63   13.808%   $231.7472   $231.75   $231.75   $231.70  
  Purchase #2 $244.80   3.670%   $253.7842   $253.78   $253.80   $253.80  
  Purchase #3 $23.65   8.112%   $25.5685   $25.57   $25.55   $25.60  
  Purchase #4 $198.69   5.541%   $209.6994   $209.70   $209.70   $209.70  
  Purchase #5 $153.27   6.730%   $163.5851   $163.59   $163.60   $163.60  
  Purchase #6 $250.62   13.764%   $285.1153   $285.12   $285.10   $285.10  
  Purchase #7 $83.52   4.404%   $87.1982   $87.20   $87.20   $87.20  
  7 purchase totals = $1,158.18       $1,256.6979   $1,256.71   $1,256.70   $1,256.70