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 $141.32   7.246%   $151.56   $151.56   $151.55   $151.60  
  Purchase #2 $181.28   13.129%   $205.0803   $205.08   $205.10   $205.10  
  Purchase #3 $218.90   10.195%   $241.2169   $241.22   $241.20   $241.20  
  Purchase #4 $239.88   13.290%   $271.7601   $271.76   $271.75   $271.80  
  Purchase #5 $14.95   12.658%   $16.8424   $16.84   $16.85   $16.80  
  Purchase #6 $170.59   11.708%   $190.5627   $190.56   $190.55   $190.60  
  Purchase #7 $82.59   7.246%   $88.5745   $88.57   $88.55   $88.60  
  7 purchase totals = $1,049.51       $1,165.5969   $1,165.59   $1,165.55   $1,165.70