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 $234.46   7.260%   $251.4818   $251.48   $251.50   $251.50  
  Purchase #2 $167.36   13.279%   $189.5837   $189.58   $189.60   $189.60  
  Purchase #3 $156.66   4.399%   $163.5515   $163.55   $163.55   $163.60  
  Purchase #4 $31.76   13.497%   $36.0466   $36.05   $36.05   $36.00  
  Purchase #5 $26.33   11.383%   $29.3271   $29.33   $29.35   $29.30  
  Purchase #6 $184.35   7.302%   $197.8112   $197.81   $197.80   $197.80  
  Purchase #7 $191.30   8.644%   $207.836   $207.84   $207.85   $207.80  
  7 purchase totals = $992.22       $1,075.6379   $1,075.64   $1,075.70   $1,075.60