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 $108.94   9.306%   $119.078   $119.08   $119.10   $119.10  
  Purchase #2 $149.26   11.627%   $166.6145   $166.61   $166.60   $166.60  
  Purchase #3 $48.84   8.837%   $53.156   $53.16   $53.15   $53.20  
  Purchase #4 $65.60   8.633%   $71.2632   $71.26   $71.25   $71.30  
  Purchase #5 $244.86   8.797%   $266.4003   $266.40   $266.40   $266.40  
  Purchase #6 $123.32   12.147%   $138.2997   $138.30   $138.30   $138.30  
  Purchase #7 $219.93   13.224%   $249.0135   $249.01   $249.00   $249.00  
  7 purchase totals = $960.75       $1,063.8252   $1,063.82   $1,063.80   $1,063.90