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 $68.68   9.580%   $75.2595   $75.26   $75.25   $75.30  
  Purchase #2 $216.52   6.626%   $230.8666   $230.87   $230.85   $230.90  
  Purchase #3 $241.29   11.547%   $269.1518   $269.15   $269.15   $269.20  
  Purchase #4 $171.76   6.210%   $182.4263   $182.43   $182.45   $182.40  
  Purchase #5 $129.77   13.436%   $147.2059   $147.21   $147.20   $147.20  
  Purchase #6 $185.39   6.540%   $197.5145   $197.51   $197.50   $197.50  
  Purchase #7 $173.75   13.765%   $197.6667   $197.67   $197.65   $197.70  
  7 purchase totals = $1,187.16       $1,300.0913   $1,300.10   $1,300.05   $1,300.20