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 $91.25   5.776%   $96.5206   $96.52   $96.50   $96.50  
  Purchase #2 $230.44   13.412%   $261.3466   $261.35   $261.35   $261.30  
  Purchase #3 $225.96   9.124%   $246.5766   $246.58   $246.60   $246.60  
  Purchase #4 $154.74   12.681%   $174.3626   $174.36   $174.35   $174.40  
  Purchase #5 $104.95   4.433%   $109.6024   $109.60   $109.60   $109.60  
  Purchase #6 $103.84   13.819%   $118.1896   $118.19   $118.20   $118.20  
  Purchase #7 $181.44   8.570%   $196.9894   $196.99   $197.00   $197.00  
  7 purchase totals = $1,092.62       $1,203.5878   $1,203.59   $1,203.60   $1,203.60