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 $159.40   4.735%   $166.9476   $166.95   $166.95   $166.90  
  Purchase #2 $240.27   6.485%   $255.8515   $255.85   $255.85   $255.90  
  Purchase #3 $157.34   11.479%   $175.4011   $175.40   $175.40   $175.40  
  Purchase #4 $54.77   6.304%   $58.2227   $58.22   $58.20   $58.20  
  Purchase #5 $241.52   13.426%   $273.9465   $273.95   $273.95   $273.90  
  Purchase #6 $177.44   11.348%   $197.5759   $197.58   $197.60   $197.60  
  Purchase #7 $13.28   12.485%   $14.938   $14.94   $14.95   $14.90  
  7 purchase totals = $1,044.02       $1,142.8833   $1,142.89   $1,142.90   $1,142.80