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 $150.34   7.869%   $162.1703   $162.17   $162.15   $162.20  
  Purchase #2 $165.43   5.148%   $173.9463   $173.95   $173.95   $173.90  
  Purchase #3 $53.85   11.610%   $60.102   $60.10   $60.10   $60.10  
  Purchase #4 $179.55   13.800%   $204.3279   $204.33   $204.35   $204.30  
  Purchase #5 $123.65   9.184%   $135.006   $135.01   $135.00   $135.00  
  Purchase #6 $161.51   6.737%   $172.3909   $172.39   $172.40   $172.40  
  Purchase #7 $147.37   12.825%   $166.2702   $166.27   $166.25   $166.30  
  7 purchase totals = $981.70       $1,074.2136   $1,074.22   $1,074.20   $1,074.20