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 $230.80   5.716%   $243.9925   $243.99   $244.00   $244.00  
  Purchase #2 $189.84   8.372%   $205.7334   $205.73   $205.75   $205.70  
  Purchase #3 $46.78   12.152%   $52.4647   $52.46   $52.45   $52.50  
  Purchase #4 $152.66   7.283%   $163.7782   $163.78   $163.80   $163.80  
  Purchase #5 $159.25   5.618%   $168.1967   $168.20   $168.20   $168.20  
  Purchase #6 $169.94   5.340%   $179.0148   $179.01   $179.00   $179.00  
  Purchase #7 $138.33   5.252%   $145.5951   $145.60   $145.60   $145.60  
  7 purchase totals = $1,087.60       $1,158.7754   $1,158.77   $1,158.80   $1,158.80