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 $184.58   10.436%   $203.8428   $203.84   $203.85   $203.80  
  Purchase #2 $94.52   12.472%   $106.3085   $106.31   $106.30   $106.30  
  Purchase #3 $93.68   4.778%   $98.156   $98.16   $98.15   $98.20  
  Purchase #4 $230.57   7.801%   $248.5568   $248.56   $248.55   $248.60  
  Purchase #5 $202.81   10.553%   $224.2125   $224.21   $224.20   $224.20  
  Purchase #6 $117.40   11.231%   $130.5852   $130.59   $130.60   $130.60  
  Purchase #7 $28.85   10.444%   $31.8631   $31.86   $31.85   $31.90  
  7 purchase totals = $952.41       $1,043.5249   $1,043.53   $1,043.50   $1,043.60