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 $152.27   5.707%   $160.96   $160.96   $160.95   $161.00  
  Purchase #2 $75.76   6.732%   $80.8602   $80.86   $80.85   $80.90  
  Purchase #3 $9.57   6.637%   $10.2052   $10.21   $10.20   $10.20  
  Purchase #4 $117.52   10.525%   $129.889   $129.89   $129.90   $129.90  
  Purchase #5 $122.27   5.402%   $128.875   $128.88   $128.90   $128.90  
  Purchase #6 $165.60   4.169%   $172.5039   $172.50   $172.50   $172.50  
  Purchase #7 $115.30   8.835%   $125.4868   $125.49   $125.50   $125.50  
  7 purchase totals = $758.29       $808.7801   $808.79   $808.80   $808.90