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 $193.52   6.560%   $206.2149   $206.21   $206.20   $206.20  
  Purchase #2 $193.89   4.486%   $202.5879   $202.59   $202.60   $202.60  
  Purchase #3 $219.59   7.633%   $236.3513   $236.35   $236.35   $236.40  
  Purchase #4 $49.71   4.637%   $52.0151   $52.02   $52.00   $52.00  
  Purchase #5 $16.75   3.300%   $17.3028   $17.30   $17.30   $17.30  
  Purchase #6 $156.58   6.507%   $166.7687   $166.77   $166.75   $166.80  
  Purchase #7 $164.92   6.425%   $175.5161   $175.52   $175.50   $175.50  
  7 purchase totals = $994.96       $1,056.7568   $1,056.76   $1,056.70   $1,056.80