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 $145.64   13.305%   $165.0174   $165.02   $165.00   $165.00  
  Purchase #2 $57.28   4.403%   $59.802   $59.80   $59.80   $59.80  
  Purchase #3 $203.37   7.384%   $218.3868   $218.39   $218.40   $218.40  
  Purchase #4 $184.26   5.705%   $194.772   $194.77   $194.75   $194.80  
  Purchase #5 $160.53   13.233%   $181.7729   $181.77   $181.75   $181.80  
  Purchase #6 $89.72   12.810%   $101.2131   $101.21   $101.20   $101.20  
  Purchase #7 $218.60   9.339%   $239.0151   $239.02   $239.00   $239.00  
  7 purchase totals = $1,059.40       $1,159.9793   $1,159.98   $1,159.90   $1,160.00