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 $145.95   3.469%   $151.013   $151.01   $151.00   $151.00  
  Purchase #2 $55.55   9.804%   $60.9961   $61.00   $61.00   $61.00  
  Purchase #3 $108.80   8.845%   $118.4234   $118.42   $118.40   $118.40  
  Purchase #4 $235.88   5.783%   $249.5209   $249.52   $249.50   $249.50  
  Purchase #5 $125.32   9.674%   $137.4435   $137.44   $137.45   $137.40  
  Purchase #6 $80.76   10.306%   $89.0831   $89.08   $89.10   $89.10  
  Purchase #7 $213.42   7.200%   $228.7862   $228.79   $228.80   $228.80  
  7 purchase totals = $965.68       $1,035.2662   $1,035.26   $1,035.25   $1,035.20