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 $73.34   3.861%   $76.1717   $76.17   $76.15   $76.20  
  Purchase #2 $215.52   12.212%   $241.8393   $241.84   $241.85   $241.80  
  Purchase #3 $193.38   5.360%   $203.7452   $203.75   $203.75   $203.70  
  Purchase #4 $237.88   6.325%   $252.9259   $252.93   $252.95   $252.90  
  Purchase #5 $180.32   6.842%   $192.6575   $192.66   $192.65   $192.70  
  Purchase #6 $112.32   8.272%   $121.6111   $121.61   $121.60   $121.60  
  Purchase #7 $219.35   8.718%   $238.4729   $238.47   $238.45   $238.50  
  7 purchase totals = $1,232.11       $1,327.4236   $1,327.43   $1,327.40   $1,327.40