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 $150.76   10.668%   $166.8431   $166.84   $166.85   $166.80  
  Purchase #2 $74.58   12.291%   $83.7466   $83.75   $83.75   $83.70  
  Purchase #3 $165.33   6.222%   $175.6168   $175.62   $175.60   $175.60  
  Purchase #4 $134.43   8.124%   $145.3511   $145.35   $145.35   $145.40  
  Purchase #5 $80.84   7.869%   $87.2013   $87.20   $87.20   $87.20  
  Purchase #6 $210.89   5.551%   $222.5965   $222.60   $222.60   $222.60  
  Purchase #7 $110.80   7.554%   $119.1698   $119.17   $119.15   $119.20  
  7 purchase totals = $927.63       $1,000.5252   $1,000.53   $1,000.50   $1,000.50