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 $49.36   7.246%   $52.9366   $52.94   $52.95   $52.90  
  Purchase #2 $192.87   4.816%   $202.1586   $202.16   $202.15   $202.20  
  Purchase #3 $226.98   10.363%   $250.5019   $250.50   $250.50   $250.50  
  Purchase #4 $240.95   11.362%   $268.3267   $268.33   $268.35   $268.30  
  Purchase #5 $173.93   10.445%   $192.097   $192.10   $192.10   $192.10  
  Purchase #6 $34.29   9.288%   $37.4749   $37.47   $37.45   $37.50  
  Purchase #7 $50.65   6.488%   $53.9362   $53.94   $53.95   $53.90  
  7 purchase totals = $969.03       $1,057.4319   $1,057.44   $1,057.45   $1,057.40