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 $129.89   11.852%   $145.2846   $145.28   $145.30   $145.30  
  Purchase #2 $176.39   4.828%   $184.9061   $184.91   $184.90   $184.90  
  Purchase #3 $234.37   9.837%   $257.425   $257.43   $257.45   $257.40  
  Purchase #4 $147.55   4.162%   $153.691   $153.69   $153.70   $153.70  
  Purchase #5 $205.65   11.874%   $230.0689   $230.07   $230.05   $230.10  
  Purchase #6 $235.56   13.514%   $267.3936   $267.39   $267.40   $267.40  
  Purchase #7 $95.76   6.590%   $102.0706   $102.07   $102.05   $102.10  
  7 purchase totals = $1,225.17       $1,340.8398   $1,340.84   $1,340.85   $1,340.90