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 $56.99   4.701%   $59.6691   $59.67   $59.65   $59.70  
  Purchase #2 $57.30   9.147%   $62.5412   $62.54   $62.55   $62.50  
  Purchase #3 $139.34   11.806%   $155.7905   $155.79   $155.80   $155.80  
  Purchase #4 $247.65   8.630%   $269.0222   $269.02   $269.00   $269.00  
  Purchase #5 $191.96   6.241%   $203.9402   $203.94   $203.95   $203.90  
  Purchase #6 $223.93   5.107%   $235.3661   $235.37   $235.35   $235.40  
  Purchase #7 $150.47   8.183%   $162.783   $162.78   $162.80   $162.80  
  7 purchase totals = $1,067.64       $1,149.1123   $1,149.11   $1,149.10   $1,149.10