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 $225.27   3.248%   $232.5868   $232.59   $232.60   $232.60  
  Purchase #2 $98.42   4.535%   $102.8833   $102.88   $102.90   $102.90  
  Purchase #3 $206.43   13.519%   $234.3373   $234.34   $234.35   $234.30  
  Purchase #4 $250.44   9.334%   $273.8161   $273.82   $273.80   $273.80  
  Purchase #5 $32.45   4.125%   $33.7886   $33.79   $33.80   $33.80  
  Purchase #6 $219.98   12.451%   $247.3697   $247.37   $247.35   $247.40  
  Purchase #7 $230.74   5.841%   $244.2175   $244.22   $244.20   $244.20  
  7 purchase totals = $1,263.73       $1,368.9993   $1,369.01   $1,369.00   $1,369.00