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 $96.58   13.732%   $109.8424   $109.84   $109.85   $109.80  
  Purchase #2 $202.63   11.202%   $225.3286   $225.33   $225.35   $225.30  
  Purchase #3 $106.36   6.666%   $113.45   $113.45   $113.45   $113.50  
  Purchase #4 $232.75   7.497%   $250.1993   $250.20   $250.20   $250.20  
  Purchase #5 $242.96   3.753%   $252.0783   $252.08   $252.10   $252.10  
  Purchase #6 $76.52   11.309%   $85.1736   $85.17   $85.15   $85.20  
  Purchase #7 $63.73   9.590%   $69.8417   $69.84   $69.85   $69.80  
  7 purchase totals = $1,021.53       $1,105.9139   $1,105.91   $1,105.95   $1,105.90