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 $54.37   8.423%   $58.9496   $58.95   $58.95   $58.90  
  Purchase #2 $181.35   9.497%   $198.5728   $198.57   $198.55   $198.60  
  Purchase #3 $167.91   6.511%   $178.8426   $178.84   $178.85   $178.80  
  Purchase #4 $150.79   6.869%   $161.1478   $161.15   $161.15   $161.10  
  Purchase #5 $57.91   4.255%   $60.3741   $60.37   $60.35   $60.40  
  Purchase #6 $143.74   6.210%   $152.6663   $152.67   $152.65   $152.70  
  Purchase #7 $170.51   11.452%   $190.0368   $190.04   $190.05   $190.00  
  7 purchase totals = $926.58       $1,000.5900   $1,000.59   $1,000.55   $1,000.50