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 $183.70   11.571%   $204.9559   $204.96   $204.95   $205.00  
  Purchase #2 $42.52   3.745%   $44.1124   $44.11   $44.10   $44.10  
  Purchase #3 $181.47   11.224%   $201.8382   $201.84   $201.85   $201.80  
  Purchase #4 $114.30   4.786%   $119.7704   $119.77   $119.75   $119.80  
  Purchase #5 $191.58   12.145%   $214.8474   $214.85   $214.85   $214.80  
  Purchase #6 $9.39   4.284%   $9.7923   $9.79   $9.80   $9.80  
  Purchase #7 $230.62   3.604%   $238.9315   $238.93   $238.95   $238.90  
  7 purchase totals = $953.58       $1,034.2481   $1,034.25   $1,034.25   $1,034.20