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 $244.65   3.374%   $252.9045   $252.90   $252.90   $252.90  
  Purchase #2 $87.48   11.285%   $97.3521   $97.35   $97.35   $97.40  
  Purchase #3 $68.47   3.843%   $71.1013   $71.10   $71.10   $71.10  
  Purchase #4 $147.76   13.820%   $168.1804   $168.18   $168.20   $168.20  
  Purchase #5 $248.51   4.640%   $260.0409   $260.04   $260.05   $260.00  
  Purchase #6 $84.52   4.788%   $88.5668   $88.57   $88.55   $88.60  
  Purchase #7 $106.94   3.201%   $110.3631   $110.36   $110.35   $110.40  
  7 purchase totals = $988.33       $1,048.5091   $1,048.50   $1,048.50   $1,048.60