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 $130.27   11.840%   $145.694   $145.69   $145.70   $145.70  
  Purchase #2 $168.83   7.670%   $181.7793   $181.78   $181.80   $181.80  
  Purchase #3 $160.54   5.714%   $169.7133   $169.71   $169.70   $169.70  
  Purchase #4 $247.83   9.422%   $271.1805   $271.18   $271.20   $271.20  
  Purchase #5 $185.37   11.435%   $206.5671   $206.57   $206.55   $206.60  
  Purchase #6 $245.50   3.511%   $254.1195   $254.12   $254.10   $254.10  
  Purchase #7 $150.92   10.771%   $167.1756   $167.18   $167.20   $167.20  
  7 purchase totals = $1,289.26       $1,396.2293   $1,396.23   $1,396.25   $1,396.30