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 $227.82   7.311%   $244.4759   $244.48   $244.50   $244.50  
  Purchase #2 $147.58   13.385%   $167.3336   $167.33   $167.35   $167.30  
  Purchase #3 $107.72   7.678%   $115.9907   $115.99   $116.00   $116.00  
  Purchase #4 $73.33   13.439%   $83.1848   $83.18   $83.20   $83.20  
  Purchase #5 $138.86   8.492%   $150.652   $150.65   $150.65   $150.70  
  Purchase #6 $184.49   13.695%   $209.7559   $209.76   $209.75   $209.80  
  Purchase #7 $41.41   7.693%   $44.5957   $44.60   $44.60   $44.60  
  7 purchase totals = $921.21       $1,015.9886   $1,015.99   $1,016.05   $1,016.10