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 $44.43   3.546%   $46.0055   $46.01   $46.00   $46.00  
  Purchase #2 $204.43   10.501%   $225.8972   $225.90   $225.90   $225.90  
  Purchase #3 $9.88   6.832%   $10.555   $10.56   $10.55   $10.60  
  Purchase #4 $91.39   7.262%   $98.0267   $98.03   $98.05   $98.00  
  Purchase #5 $11.52   7.740%   $12.4116   $12.41   $12.40   $12.40  
  Purchase #6 $71.91   11.559%   $80.2221   $80.22   $80.20   $80.20  
  Purchase #7 $166.73   6.774%   $178.0243   $178.02   $178.00   $178.00  
  7 purchase totals = $600.29       $651.1424   $651.15   $651.10   $651.10