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 $190.43   6.229%   $202.2919   $202.29   $202.30   $202.30  
  Purchase #2 $49.62   9.280%   $54.2247   $54.22   $54.20   $54.20  
  Purchase #3 $98.70   12.751%   $111.2852   $111.29   $111.30   $111.30  
  Purchase #4 $83.63   6.436%   $89.0124   $89.01   $89.00   $89.00  
  Purchase #5 $241.70   4.501%   $252.5789   $252.58   $252.60   $252.60  
  Purchase #6 $38.61   5.232%   $40.6301   $40.63   $40.65   $40.60  
  Purchase #7 $180.60   13.476%   $204.9377   $204.94   $204.95   $204.90  
  7 purchase totals = $883.29       $954.9609   $954.96   $955.00   $954.90