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 $52.88   12.142%   $59.3007   $59.30   $59.30   $59.30  
  Purchase #2 $227.39   5.708%   $240.3694   $240.37   $240.35   $240.40  
  Purchase #3 $184.40   7.720%   $198.6357   $198.64   $198.65   $198.60  
  Purchase #4 $196.26   3.333%   $202.8013   $202.80   $202.80   $202.80  
  Purchase #5 $136.43   7.831%   $147.1138   $147.11   $147.10   $147.10  
  Purchase #6 $172.47   5.701%   $182.3025   $182.30   $182.30   $182.30  
  Purchase #7 $99.59   4.143%   $103.716   $103.72   $103.70   $103.70  
  7 purchase totals = $1,069.42       $1,134.2394   $1,134.24   $1,134.20   $1,134.20