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 $61.41   11.812%   $68.6637   $68.66   $68.65   $68.70  
  Purchase #2 $176.39   4.104%   $183.629   $183.63   $183.65   $183.60  
  Purchase #3 $200.50   12.247%   $225.0552   $225.06   $225.05   $225.10  
  Purchase #4 $172.99   11.755%   $193.325   $193.33   $193.35   $193.30  
  Purchase #5 $39.66   5.310%   $41.7659   $41.77   $41.75   $41.80  
  Purchase #6 $176.47   12.595%   $198.6964   $198.70   $198.70   $198.70  
  Purchase #7 $233.29   4.194%   $243.0742   $243.07   $243.05   $243.10  
  7 purchase totals = $1,060.71       $1,154.2094   $1,154.22   $1,154.20   $1,154.30