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 $152.97   9.570%   $167.6092   $167.61   $167.60   $167.60  
  Purchase #2 $172.91   10.271%   $190.6696   $190.67   $190.65   $190.70  
  Purchase #3 $246.26   9.821%   $270.4452   $270.45   $270.45   $270.40  
  Purchase #4 $240.80   5.771%   $254.6966   $254.70   $254.70   $254.70  
  Purchase #5 $84.70   5.634%   $89.472   $89.47   $89.45   $89.50  
  Purchase #6 $117.44   7.286%   $125.9967   $126.00   $126.00   $126.00  
  Purchase #7 $65.58   8.744%   $71.3143   $71.31   $71.30   $71.30  
  7 purchase totals = $1,080.66       $1,170.2036   $1,170.21   $1,170.15   $1,170.20