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 $174.77   5.442%   $184.281   $184.28   $184.30   $184.30  
  Purchase #2 $219.29   4.297%   $228.7129   $228.71   $228.70   $228.70  
  Purchase #3 $58.35   8.804%   $63.4871   $63.49   $63.50   $63.50  
  Purchase #4 $244.48   11.783%   $273.2871   $273.29   $273.30   $273.30  
  Purchase #5 $119.49   13.573%   $135.7084   $135.71   $135.70   $135.70  
  Purchase #6 $134.28   6.709%   $143.2888   $143.29   $143.30   $143.30  
  Purchase #7 $225.26   6.757%   $240.4808   $240.48   $240.50   $240.50  
  7 purchase totals = $1,175.92       $1,269.2461   $1,269.25   $1,269.30   $1,269.30