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 $62.46   12.402%   $70.2063   $70.21   $70.20   $70.20  
  Purchase #2 $55.59   9.678%   $60.97   $60.97   $60.95   $61.00  
  Purchase #3 $245.88   8.679%   $267.2199   $267.22   $267.20   $267.20  
  Purchase #4 $106.94   8.281%   $115.7957   $115.80   $115.80   $115.80  
  Purchase #5 $145.86   6.607%   $155.497   $155.50   $155.50   $155.50  
  Purchase #6 $212.41   6.498%   $226.2124   $226.21   $226.20   $226.20  
  Purchase #7 $152.34   13.398%   $172.7505   $172.75   $172.75   $172.80  
  7 purchase totals = $981.48       $1,068.6518   $1,068.66   $1,068.60   $1,068.70