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 $180.96   13.259%   $204.9535   $204.95   $204.95   $205.00  
  Purchase #2 $235.28   6.745%   $251.1496   $251.15   $251.15   $251.10  
  Purchase #3 $155.31   6.710%   $165.7313   $165.73   $165.75   $165.70  
  Purchase #4 $224.29   12.676%   $252.721   $252.72   $252.70   $252.70  
  Purchase #5 $132.65   6.259%   $140.9526   $140.95   $140.95   $141.00  
  Purchase #6 $51.85   9.547%   $56.8001   $56.80   $56.80   $56.80  
  Purchase #7 $34.52   8.861%   $37.5788   $37.58   $37.60   $37.60  
  7 purchase totals = $1,014.86       $1,109.8869   $1,109.88   $1,109.90   $1,109.90