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 $36.52   5.250%   $38.4373   $38.44   $38.45   $38.40  
  Purchase #2 $197.27   5.189%   $207.5063   $207.51   $207.50   $207.50  
  Purchase #3 $129.44   4.257%   $134.9503   $134.95   $134.95   $135.00  
  Purchase #4 $218.29   13.418%   $247.5802   $247.58   $247.60   $247.60  
  Purchase #5 $198.29   13.565%   $225.188   $225.19   $225.20   $225.20  
  Purchase #6 $130.32   4.167%   $135.7504   $135.75   $135.75   $135.80  
  Purchase #7 $28.34   3.555%   $29.3475   $29.35   $29.35   $29.30  
  7 purchase totals = $938.47       $1,018.7600   $1,018.77   $1,018.80   $1,018.80