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 $50.61   6.639%   $53.97   $53.97   $53.95   $54.00  
  Purchase #2 $59.52   13.611%   $67.6213   $67.62   $67.60   $67.60  
  Purchase #3 $143.68   5.349%   $151.3654   $151.37   $151.35   $151.40  
  Purchase #4 $26.52   3.534%   $27.4572   $27.46   $27.45   $27.50  
  Purchase #5 $214.77   12.308%   $241.2039   $241.20   $241.20   $241.20  
  Purchase #6 $20.93   6.538%   $22.2984   $22.30   $22.30   $22.30  
  Purchase #7 $211.30   9.805%   $232.018   $232.02   $232.00   $232.00  
  7 purchase totals = $727.33       $795.9342   $795.94   $795.85   $796.00