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 $216.27   12.560%   $243.4335   $243.43   $243.45   $243.40  
  Purchase #2 $95.52   10.540%   $105.5878   $105.59   $105.60   $105.60  
  Purchase #3 $198.54   4.258%   $206.9938   $206.99   $207.00   $207.00  
  Purchase #4 $32.30   11.470%   $36.0048   $36.00   $36.00   $36.00  
  Purchase #5 $36.40   5.290%   $38.3256   $38.33   $38.35   $38.30  
  Purchase #6 $172.74   7.472%   $185.6471   $185.65   $185.65   $185.60  
  Purchase #7 $199.77   9.831%   $219.4094   $219.41   $219.40   $219.40  
  7 purchase totals = $951.54       $1,035.4020   $1,035.40   $1,035.45   $1,035.30