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 $149.89   7.617%   $161.3071   $161.31   $161.30   $161.30  
  Purchase #2 $183.95   13.268%   $208.3565   $208.36   $208.35   $208.40  
  Purchase #3 $246.70   12.519%   $277.5844   $277.58   $277.60   $277.60  
  Purchase #4 $99.84   7.675%   $107.5027   $107.50   $107.50   $107.50  
  Purchase #5 $43.52   7.495%   $46.7818   $46.78   $46.80   $46.80  
  Purchase #6 $109.25   10.470%   $120.6885   $120.69   $120.70   $120.70  
  Purchase #7 $91.41   11.709%   $102.1132   $102.11   $102.10   $102.10  
  7 purchase totals = $924.56       $1,024.3342   $1,024.33   $1,024.35   $1,024.40