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 $204.65   12.658%   $230.5546   $230.55   $230.55   $230.60  
  Purchase #2 $140.68   7.132%   $150.7133   $150.71   $150.70   $150.70  
  Purchase #3 $131.29   12.205%   $147.3139   $147.31   $147.30   $147.30  
  Purchase #4 $56.61   5.150%   $59.5254   $59.53   $59.55   $59.50  
  Purchase #5 $57.61   4.659%   $60.294   $60.29   $60.30   $60.30  
  Purchase #6 $103.85   10.760%   $115.0243   $115.02   $115.00   $115.00  
  Purchase #7 $163.48   10.793%   $181.1244   $181.12   $181.10   $181.10  
  7 purchase totals = $858.17       $944.5499   $944.53   $944.50   $944.50