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 $235.49   11.837%   $263.365   $263.37   $263.35   $263.40  
  Purchase #2 $118.85   6.440%   $126.5039   $126.50   $126.50   $126.50  
  Purchase #3 $44.60   6.123%   $47.3309   $47.33   $47.35   $47.30  
  Purchase #4 $69.79   5.658%   $73.7387   $73.74   $73.75   $73.70  
  Purchase #5 $243.60   8.777%   $264.9808   $264.98   $265.00   $265.00  
  Purchase #6 $27.90   11.556%   $31.1241   $31.12   $31.10   $31.10  
  Purchase #7 $224.85   8.508%   $243.9802   $243.98   $244.00   $244.00  
  7 purchase totals = $965.08       $1,051.0236   $1,051.02   $1,051.05   $1,051.00