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 $195.86   6.464%   $208.5204   $208.52   $208.50   $208.50  
  Purchase #2 $198.51   11.799%   $221.9322   $221.93   $221.95   $221.90  
  Purchase #3 $159.93   9.409%   $174.9778   $174.98   $175.00   $175.00  
  Purchase #4 $27.26   8.581%   $29.5992   $29.60   $29.60   $29.60  
  Purchase #5 $140.35   3.722%   $145.5738   $145.57   $145.55   $145.60  
  Purchase #6 $81.59   12.125%   $91.4828   $91.48   $91.50   $91.50  
  Purchase #7 $146.35   13.746%   $166.4673   $166.47   $166.45   $166.50  
  7 purchase totals = $949.85       $1,038.5535   $1,038.55   $1,038.55   $1,038.60