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 $48.65   6.353%   $51.7407   $51.74   $51.75   $51.70  
  Purchase #2 $73.99   11.280%   $82.3361   $82.34   $82.35   $82.30  
  Purchase #3 $136.42   5.229%   $143.5534   $143.55   $143.55   $143.60  
  Purchase #4 $115.49   6.230%   $122.685   $122.69   $122.70   $122.70  
  Purchase #5 $225.80   6.702%   $240.9331   $240.93   $240.95   $240.90  
  Purchase #6 $143.49   5.224%   $150.9859   $150.99   $151.00   $151.00  
  Purchase #7 $224.74   8.210%   $243.1912   $243.19   $243.20   $243.20  
  7 purchase totals = $968.58       $1,035.4254   $1,035.43   $1,035.50   $1,035.40