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 $144.51   8.386%   $156.6286   $156.63   $156.65   $156.60  
  Purchase #2 $204.86   12.661%   $230.7973   $230.80   $230.80   $230.80  
  Purchase #3 $197.37   11.294%   $219.661   $219.66   $219.65   $219.70  
  Purchase #4 $84.64   8.205%   $91.5847   $91.58   $91.60   $91.60  
  Purchase #5 $205.85   12.230%   $231.0255   $231.03   $231.05   $231.00  
  Purchase #6 $136.51   3.532%   $141.3315   $141.33   $141.35   $141.30  
  Purchase #7 $207.66   12.123%   $232.8346   $232.83   $232.85   $232.80  
  7 purchase totals = $1,181.40       $1,303.8632   $1,303.86   $1,303.95   $1,303.80