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 $244.80   12.607%   $275.6619   $275.66   $275.65   $275.70  
  Purchase #2 $59.85   10.277%   $66.0008   $66.00   $66.00   $66.00  
  Purchase #3 $107.46   5.720%   $113.6067   $113.61   $113.60   $113.60  
  Purchase #4 $201.29   4.705%   $210.7607   $210.76   $210.75   $210.80  
  Purchase #5 $204.51   7.535%   $219.9198   $219.92   $219.90   $219.90  
  Purchase #6 $145.50   11.842%   $162.7301   $162.73   $162.75   $162.70  
  Purchase #7 $74.61   6.148%   $79.197   $79.20   $79.20   $79.20  
  7 purchase totals = $1,038.02       $1,127.8770   $1,127.88   $1,127.85   $1,127.90